#help-49

1 messages · Page 266 of 1

buoyant fjord
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oh yeah

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bruh

junior flower
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and also…

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that sequence needs to converge to the same thing for every such (x_n)

buoyant fjord
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oh yeah

junior flower
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that sequence converging to 0 for any (x_n) for your specific problem and what i said here are very related

buoyant fjord
#

wait one sec im trying something

radiant roost
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why are you using two sequences?

junior flower
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because the slope of that secant line is the value (f(b) - f(a))/(b-a)

buoyant fjord
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theres the x_n sequence and the difference quotient sequence

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wait so i want

junior flower
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and that value converge to 0 when you take b values close to -2

buoyant fjord
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an N such that for all n>N $d(x_n,-2)<d(x,-2)/2$ maybe lemme try it

grand pondBOT
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Julian

buoyant fjord
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eh

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thats not gonna work cuz its weird yeah

junior flower
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let me ask you something. if the function was instead defined by f(x) = 3(x+2)^2 for all real x, would you be able to show, using the sequence interpretation, that f is differentiable at 0?

buoyant fjord
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yeah cuz

junior flower
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ok now i’m going to tell you that it’s very easy to adjust that proof to apply to your problem too

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because…

buoyant fjord
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product or smth

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?

junior flower
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when you take an irrational point, the secant line expression is 0

buoyant fjord
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yeah

radiant roost
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yeah it's not a product, it's cases

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case 1, if it's irrational then it's 0 and it's in a certain range
case 2, if it's rational then it takes a certain value and u have to show that's in the range too

buoyant fjord
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i thought the irrational case was trivial right

junior flower
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yes

radiant roost
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yes but you still have to state it

buoyant fjord
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i am yea

radiant roost
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i mean if you're doing a proof

buoyant fjord
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i will include it

radiant roost
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yeah but i can't understand using two sequences, i think you just need to take one arbitrary sequence and show that its limit is 0

buoyant fjord
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im doing an arbitrary mixed one]

radiant roost
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what is a mixed sequence?

buoyant fjord
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like with irrational and rational

junior flower
radiant roost
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do you mean that a_n and b_n are subsequences?

buoyant fjord
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for irrationals

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so thats less than whatever epsilon

buoyant fjord
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3(x_n+2)^2's limit?

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cuz the division

junior flower
radiant roost
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shouldn't it converge to -2?

buoyant fjord
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it does but the difference quotient converges to 0 is what we wanna show

junior flower
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(x_n) does by assumption

junior flower
radiant roost
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you said it converges to a

buoyant fjord
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well a is -2 i think

junior flower
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yea

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i was just using the notation from here

buoyant fjord
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oh yeah

radiant roost
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what is b?

buoyant fjord
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wheres b

radiant roost
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^

buoyant fjord
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oh thats unrelated

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i was showing an example of my messy solutions

radiant roost
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oh

buoyant fjord
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the original problem is

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here

radiant roost
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right, ok

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carry on

buoyant fjord
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oh i can prob just assume the limit cuz we had this on an older homework

junior flower
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if you have that the quotient limit is 0 with rational x_n’s, it’s easy to say it’s all 0 with irrational x_n’s too

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since the quotient is 0 when x_n is irrational

buoyant fjord
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alright i think i got it thanks

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peace

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.close

midnight plankBOT
#
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junior flower
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great

midnight plankBOT
#
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tidal turret
midnight plankBOT
grand pondBOT
#

Renato

lyric charm
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where is your question

tidal turret
#

can someone explain what does this mean?

lyric charm
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there's several different points that could demand explanation

tidal turret
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i just find it confusing

lyric charm
# tidal turret

can you at least narrow down to which of the 4 paragraphs you want explained from this picture?

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that or we could do it the painful way and i could extract this info from you like up to 4 rotten teeth

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@tidal turret

tidal turret
lyric charm
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paragraph 2 is an intuitive explanation of WOP

ripe juniper
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so

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what is the problem

tidal turret
lyric charm
tidal turret
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can we narrow it down to a down to earth example test case?

lyric charm
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suppose A is the set of all primes

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it's infinite, so big

tidal turret
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yes

lyric charm
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but. 67 is in A

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so we can narrow down to the finite set {primes <= 67} and the minimum won't change

tidal turret
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2

lyric charm
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we have freedom of choice here

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i am just giving an example

tidal turret
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okay let's try 67 and then 2 please

lyric charm
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you want this worked out formally?

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it will be very boring and not remotely enlightening

tidal turret
lyric charm
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ok then let's not

tidal turret
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this is an intro to wop

tidal turret
lyric charm
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and consider only the elements of A that are leq that one

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i translated it into plain English

tidal turret
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is tricky to follow

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why they say consider finite then consider infinite set

lyric charm
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with a finite set we can think about "iterating" over all its elements and it'll come to an end

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because. well that's the entire thing with finite sets isn't it

tidal turret
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sure

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N_<=n0 is finite

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?

midnight plankBOT
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@tidal turret Has your question been resolved?

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midnight plankBOT
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viral dagger
grand pondBOT
midnight plankBOT
viral dagger
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hold on nvm

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blue, yellow, and green are only adjacent for (528,529) (1495,1496)

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so except them, each blue, each yellow, and each green contributes 2 pairs

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so (floor(2023/23)+floor(2023/88)-floor(2023/(23×88))×2

runic hamlet
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green never occurs

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strange

viral dagger
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yeah thats what i thought

viral dagger
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anywhere i went wrong?

runic hamlet
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hmm if yes I dont see where

viral dagger
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alright then, thanks!

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.solved

midnight plankBOT
#
Channel closed

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midnight plankBOT
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lusty python
#

Hi, I needed help with set cardinalities to solve a coding problem (specifically advent of code 2025 day 5 part 2)

lusty python
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I needed to calculate $\abs{A_1 \cup A_2 \cup A_3 \dots \cup A_n}$ where $A_i$ is a finite interval of integers

grand pondBOT
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1 divided by 0 equals Infinity

gaunt jetty
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so...calculate it?

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like you want code? kekhands

lusty python
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without having to do a lot of code

gaunt jetty
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well you probably gotta use a sort and merge algorithm

lusty python
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?

gaunt jetty
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like, sort all the intervals based on their starting integer, iterate through them and merge if they overlap or touch

lusty python
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that's the problem

gaunt jetty
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well since it is sorted if they don't overlap the next one is going to be a new separate interval

lusty python
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🤯

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damn that's genius

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ty

gaunt jetty
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idk if thats sarcasm or not but ok

lusty python
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idk

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lemme try that out

cerulean oyster
lusty python
cerulean oyster
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If you had any probability class this should sound awfully similar

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but if they are independent (dont share any integer), then the cardinality of that set is the sum of the cardinalities

lusty python
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they may share any integer

cerulean oyster
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Okay, then you probably want a hash map here

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sadly you will have to iterate through all the arrays

lusty python
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maximum limit is around 15 digits

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so that won't help

cerulean oyster
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as to cardinality of individual sets?

lusty python
#
#include <iostream>
#include <cstdio>
#include <string>
#include <algorithm>

struct Range {
    size_t start;
    size_t end;
};

void push_digit(size_t &n, char digit) {
    n *= 10;
    n += digit - '0';
}

Range parse_range(std::string s) {
    size_t start = 0;
    size_t end = 0;
    bool dash = false;
    for (char &c : s) {
        if (c == '-') {
            dash = true;
        } else if (dash) {
            push_digit(end, c);
        } else {
            push_digit(start, c);
        }
    }

    return {start, end};
}

int main() {
    std::ios_base::sync_with_stdio(false);
    std::cin.tie(nullptr);
    std::cout.tie(nullptr);

    std::freopen("testfile.INP", "r", stdin);
    std::freopen("testfile.OUT", "w", stdout);

    size_t m;
    std::cin >> m;

    Range r[m];
    for (size_t i = 0; i < m; i++) {
        std::string s;
        std::cin >> s;

        r[i] = parse_range(s);
    }

    std::sort(r, r+m, [](Range a, Range b) {
        if (a.start != b.start) {
            return a.start < b.start;
        }

        return a.end < b.end;
    });

    size_t res = 0;
    Range current_interval = r[0];
    for (size_t i = 1; i < m; i++) {
        if (r[i].start <= current_interval.end) {
            current_interval.end = r[i].end;
        } else {
            res += current_interval.end - current_interval.start + 1;
            current_interval = r[i];
        }
    }

    std::cout << res + current_interval.end - current_interval.start + 1;
    return 0;
}

@gaunt jetty

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wrong answer

lusty python
cerulean oyster
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we dont really care about the values really

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just about their multiplicity (how many times they appear)

lusty python
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yeah

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but the problem is about iterating each range

cerulean oyster
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yeah no clue

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like, from the theory side, you can do the sum of all the intervals - the sum of all their intersections

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but thats O(n^2)

lusty python
subtle zinc
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isn't it an interval

cerulean oyster
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not even n^2, its n!, lmao.

pine wave
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Yeah you would want to be looking for an algorithm

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Main idea is basically a sweep-line-like algorithm

lusty python
pine wave
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You can also start from how you sorted your intervals

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And consider the subproblem of "how many elements in the union of first k intervals

lusty python
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I was thinking of that approach

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Got 2 base cases

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And don't know how to move on

cerulean oyster
# pine wave Main idea is basically a sweep-line-like algorithm

Someone correct me if im wrong, but on this

take, A1 and A2, find Union (U1) and Intersection (S1)
U1 and A3, find (U2) and (S2)
etc... until you covered all A

Un is just the union of all sets, sum(S1...Sn) should cover multiplicity of the intervals.

pine wave
cerulean oyster
#

ill draw a thing rq just to check cause im doubting myself

pine wave
pine wave
# lusty python Dp question eh?

Not very dp, simple iteration will do from k to k+1. Use the fact that you sorted your intervals. There are two (or three) cases to consider

cerulean oyster
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na i was wrong

pine wave
pine wave
cerulean oyster
#

yeah, union of previous intervals is just a loss of information

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Sorting them out and using the end-start values is prob best

lusty python
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Ill try out later

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.close

midnight plankBOT
#
Channel closed

Closed by @lusty python

Use .reopen if this was a mistake.

cerulean oyster
#

gl

midnight plankBOT
#
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hybrid sage
#

i need help in understanding the answer of this question

hybrid sage
placid abyss
#

Do you remember what a closed circle (filled in) vs open circle represents)

hybrid sage
placid abyss
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Right

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If we start with the 2nd question which is simpler

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What does the question ask for?

hybrid sage
placid abyss
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And what does that mean?

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Just in words

hybrid sage
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it's looking for -2

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or our x

placid abyss
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Yeah

hybrid sage
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but idk what answer to put

placid abyss
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Is that what you circled?

hybrid sage
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yes

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oh wait

placid abyss
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Are you sure? Look at the x-value

hybrid sage
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its the other one right

placid abyss
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Yeah,

hybrid sage
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okay

placid abyss
#

But

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At x=-2 theres two circles

hybrid sage
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so how do i look for the answer?

placid abyss
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So think about what a fuller circle means vs a non filled circle

hybrid sage
placid abyss
#

Yeah exactly

hybrid sage
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and what value is the closed circle? it doesn't indicate in the image

placid abyss
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It does say

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You can count the y-direction

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The vertical axis

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In the same way you counted x=-2 is two blocks to the left

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Apply the same concept to the y axis

hybrid sage
#

ohh

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so it would be

placid abyss
#

Did you get an answer?

hybrid sage
#

-3

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?

placid abyss
#

Not exactly. count again

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And you should start from the point where the two axes intersect

hybrid sage
#

is it a negative on the y axis?

placid abyss
#

It is negative!

hybrid sage
#

-2?

placid abyss
#

Exactly

hybrid sage
#

ahh

placid abyss
#

And now the first question

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Do you know what this limit means?

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Just in words

hybrid sage
#

am i right?

placid abyss
#

Yeah, so as x approaches -2 from LEFT to RIGHT, what does the value of x reach?

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In the same way, if it said -2^(+) it would mean the value as x approaches -2 from RIGHT to LEFT

hybrid sage
#

wouldn't - mean to the left? or is it the other way around?

placid abyss
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Other way around

hybrid sage
#

ohh so it would be to the right?

placid abyss
#

I like to think about it as: if we have a negative we start from the negative side and move in the opposite direction (so to the positive)

placid abyss
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And if we have a positive sign, we start from the positive and move in the opposite direction so towards the negatives

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This is a good thumb rule to remember

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Alright so if you start from the very left side of the graph (negative side) and move tot he positive side, and stop at x=-2 what does the graph read

hybrid sage
#

so like this?

placid abyss
#

Yup

hybrid sage
#

ohh nice

placid abyss
#

One important thing: make sure you follow the graphs line

placid abyss
#

Look at the graph

hybrid sage
#

okay so this is our -2

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and that's where we stop

placid abyss
#

You’re going the wrong way now

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You want to start in the bottom left corner

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And follow the graph to the right

hybrid sage
#

ohh

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this is our bottom left corner?

placid abyss
#

Yeah

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So you start at the very edge (left) and move to the right

hybrid sage
#

until we reach -2?

placid abyss
#

Yeah

hybrid sage
#

okay so we would stop here?

placid abyss
hybrid sage
#

like this?

placid abyss
#

Yup! But the important thing is you’d stop on the same line

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You don’t jump up/down

hybrid sage
#

and then we get the value of the closed circle?

placid abyss
#

Exactly

hybrid sage
#

so we would get -2 again?

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for the value

placid abyss
#

Yup

hybrid sage
#

ohh nice thank you for this

#

.close

midnight plankBOT
#
Channel closed

Closed by @hybrid sage

Use .reopen if this was a mistake.

#
Available help channel!

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Ask your math question in a clear, concise manner.
Show your work, and if possible, explain where you are stuck.
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• Be polite and have a nice day!

Read #❓how-to-get-help for further information on how to ask a good question, and about conduct in the question channels.

jade magnet
#

hey i dont think i understand the difference between prims and nearest neighbour

jade magnet
#

or even between prims and kruskals tbh

#

whenever i want to find a minimum spanning tree i just add the node with the smallest weighted edge that's not included in my graph if that makes sense

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but i dont even know which algorithm that is

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i dont understand the differences can somebody help

#

nvm

#

my teacher explained it

#

.solved

midnight plankBOT
#
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midnight plankBOT
#
Available help channel!

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Remember:
Ask your math question in a clear, concise manner.
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slate crater
#

Let 35 people seated in a circular table, in how many ways can we pick 6 out of 35 people given no any 2 of them sitting next to each other.

slate crater
#

The answer is $\frac{\binom{28}{5}}{\binom{35}{6}} \cdot \frac{35}{6}$

grand pondBOT
#

Poly(^///^)

lyric charm
#

wait hold on

#

do you mean "how many ways" or "what's the probability"

slate crater
#

But I don't get where the 35/6 come from

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Oh

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Mb

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Probability

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Sorry bruh the question was asked yesterday so I didn't remember it correctly

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But everything else is right

junior flower
#

so the question is what’s the probability 6 people picked at random are all not sitting next to each other?

slate crater
#

Are there a different between choosing 6 people from 35 people in a circular table and just choosing 6 from 35?

junior flower
#

what would “just choosing 6 from 35” mean?

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it would be different if they were e.g. in a line

slate crater
#

$\binom{35}{6}$ by that I mean is the the sample space?

grand pondBOT
#

Poly(^///^)

junior flower
#

because the ones on the end wouldn’t be next to each as they would be if they wrapped around in a circle

#

you can still view the sample space as something with 35 choose 6 elements

slate crater
#

Yeah that's why I asked and that what I did

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Then fix one from 6 people, then choose 5 others people from the rest give binom{28}{5} and there're 6 ways of choosing the fixed person so divide it by 6

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But where the 35 come from

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I guessed the sample space is binom{35}{6}/35 so it satisfies the answer but I couldn't wrap my head around why it's the sample space

junior flower
#

there are 35 seats you can choose to fix the first person at

slate crater
#

So the sample space is binom{35}{6}/35?

junior flower
#

it depends you how do the problem really

slate crater
slate crater
junior flower
#

there are 35 choose 6 ways to put the people around the table, but if you take a particular way and rotate it, each of the 35 rotations are kinda the same thing

#

you can treat them as the same or different and still do the problem

slate crater
#

Like what's the thought process for it

junior flower
#

if you consider tables the same under rotations, there are (35 choose 6)/35 of them and that’s where the 35 comes from under that interpretation

junior flower
#

do you know what i mean by “same under rotations”?

slate crater
gusty falcon
junior flower
#

the difference is not between linear and circular here

junior flower
slate crater
junior flower
#

imagine that you are going to sit in a circle with 3 of your friends and you wonder to yourself how many different ways you can sit down. anyway, you guys sit down some way in 4 seats. if you all move over to the right one seat, should that be considered a different circle? it’s kinda the same circle, right? but it’s also different in the sense that you are at different seats. well they could be counted as different or not, it’s really up to you

#

there are (35 choose 6)/35 tables if you consider rotations of tables to be the same and 35 choose 6 if you consider them to be different

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also generally in school it’s expected for you to treat tables that are the same up to rotation as the same

slate crater
#

Okay wao I didn't know I was that dumb

#

Okay get it

junior flower
#

you are not

slate crater
#

okay changed my mind set a bit, it makes sense now

#

One question

#

How can we do the problem with the sample space 35 choose 6?

slate crater
junior flower
slate crater
#

Okay hang on, why does the step of choosing the first seat not matter here? When in sample space we're not choosing the first seat

junior flower
#

do you mean in the tables are the same under rotations interpretation?

slate crater
#

yeah

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Oh

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okay lol

junior flower
#

because no matter where you put the first person, the table looks the same

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when they are the same under rotations

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so there’s only one table

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not 35 different ones you could make with one person

slate crater
#

Okay tbh I'm not sure what you're taking about really

junior flower
#

😭

slate crater
#

No I meant

slate crater
junior flower
#

let’s say we consider tables that are the same under rotation to be the same. no matter where i put the first person, i’m forming the same table right?

slate crater
#

yeah

junior flower
#

now let’s say we consider them different

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i can put the first person at any of the 35 seats and those tables will all be distinct

slate crater
#

okay

junior flower
#

so that’s why the placement of the first person matters in one case but not the other

slate crater
#

hmmcat but shouldn't they be different? I meant the assumptions are different

junior flower
#

what’s they

slate crater
junior flower
#

i’m not sure if this is what you’re asking, but at the end of the day the probability that the 6 people are not sitting next to each other is the same regardless of which of the two interpretations you pick. the interpretations just affect things like “the total number of tables” for calculation purposes

slate crater
#

Okay so in 35*(28 choose 5)/6

junior flower
#

if i roll some different colored 6 sided dice and ask what’s the probability they sum to 15, it doesn’t matter if i consider them all the same or distinguish them by color when looking at all the possible rolls. the probability they sum to 15 is unaffected

slate crater
#

(28 choose 5)/6 is the way that we count if the rotation doesn't matter, and we multiply it by 35 so it match with the sample space where we take 35 choose 6 where the rotation does matter

slate crater
slate crater
#

i get that...

junior flower
#

that’s why the 35 gets corrected for both in the total and in the good events

slate crater
#

But I've thought you said smth different 😭

#

Okay clearly I'm wasting your time bruh

#

Thanks for the help

junior flower
#

😭

#

no time spent in the help channels is wasted for me

slate crater
#

It does for me haha

#

Well it used to

#

Okay Imma close the channel

#

Have a nice day!!

#

.close

midnight plankBOT
#
Channel closed

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Use .reopen if this was a mistake.

junior flower
#

cya

midnight plankBOT
#
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lethal aurora
#

Hi, Im trying to understand Cramers rule better,
so essentially we plug in the output vector in a row i followed by calculating the determinant, this gives us the signed value of b
relative to our basis consisting of the column vectors. considering each coordinate get scaled by a value det(A)
we get det(A)*v = (len(b1) len(b2) ... len(bn) )
and thus vi = signed volume(bi)/det(A)
is my reasoning correct?

midnight plankBOT
#

@lethal aurora Has your question been resolved?

midnight plankBOT
#

@lethal aurora Has your question been resolved?

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blissful trench
#

A curve on a highway has a 1000 foot radus with lanes that are 14 feet wide. If the curve makes a 180 degree turn how much longer is the outside edge of the far lane than the inside edje of the close lane? This is a 3 lane highway and assume the 1000 radius is to the inside edge of the cloest lane.

blissful trench
#

dunno where to start

spiral rock
#

its the ratio of the radii

#

because of the formula pi * r for the perimeter of a half circle

blissful trench
#

ik r_1 is 1000 but idk r_2

spiral rock
#

3 lanes 14 feet

blissful trench
#

so add them?

spiral rock
#

multiply

blissful trench
#

,calc 1000143

grand pondBOT
#

Result:

42000
blissful trench
#

like this? catscream

shell wigeon
#

Add the lanes, multiply with the ratio

spiral rock
#

no like 1000 + 3 * 14

blissful trench
#

oh

#

ok got it thanks

#

.close

midnight plankBOT
#
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fossil ember
#

Okay, I have P+(O-P)t+(X-O)x+(Y-O)y=Q+sum((V_i)s_i) where all upper case are known and points except V_i which is known and a vector and all other things are scalar and unknown and for other things, t>=1 and I have ranges of what s_i can be like 2>=s_1>=1 and a minimum and maximum like that per s_i, what would be most efficient to solve this in 4d+ and 3d? I can make it like per dimension subtract Q and other than one V_i and s_i so that leaves that over V_i for one dimension. This is way overdetermined and all things are >=. What are some recommendations to study? X E.

fossil ember
#

We can also have (V_i s_i)>=V_i bound. X E.

#

There are things to do this but this is a lot. X E.

#

The end result should be x, y, and t for where the outer edges of the shape are, maybe even eliminate some back faces. X E.

#

Just looking for things to look up. X E.

#

Honestly, this is just ideas. X E.

runic hamlet
#

linear programming

fossil ember
#

LP, of course. X E.

#

Anything specific?

fossil ember
#

Well I know linear programming can but efficient algorithms?

midnight plankBOT
#

@fossil ember Has your question been resolved?

fossil ember
#

Trying for O(n), not O(n^(n^2)). X E.

runic hamlet
#

n being what? dimension?

#

not even solving linear systems is O(n)

#

and thats already basically the easiest thing ever

#

linear programming is polynomial time

fossil ember
#

Okay, n^2?

#

I don't want the second option I mentioned. X E.

runic hamlet
fossil ember
#

Yep. X E.

#

Point is I don't like long times. X E.

runic hamlet
#

polynomial time is short time

#

all things considered

fossil ember
#

Thanks for talking. X E.

#

So like what?

#

Like what theories should I study?

fossil ember
#

Estimate?

#

Well, any good books on linear programming?

fallow scarab
fossil ember
#

Well, there is one valid link in the whole years long discussion and I am unsure if it is relevant. X E.

#

Is linear programming linear algebra?

fossil ember
#

There is officially no recommended book yet. X E.

#

How is this the bottom help already?

#

Am I doomed?

fallow scarab
#

linear programming is usually beyond lower division undergrad math knowledge

fossil ember
#

Well I do Calculus before done with Precalculus in school so why not?

fallow scarab
#

good for you

fossil ember
#

Yeah, I am kind of advanced for being uneducated, or kind of uneducated for being advanced. X E.

#

Why is there no linear programming channel?

#

And why not a 4d math channel?

#

I joke. X E.

#

Anyway, any specific theories I should study?

#

I know cosine is trash in 4d+. X E.

carmine sigil
#

I'm not sure I understand your meaning here? How is it trash?

fossil ember
fossil ember
carmine sigil
#

a.b = |a| |b| cos θ still

#

That is definitely useful

fossil ember
#

I have tried the lin alg version and distances. X E.

carmine sigil
#

You already need two values to specify a direction in 3d, you just need 3 to specify a direction in 4d.

fossil ember
#

Yeah, using that, cos(ABC)•distance(AC) does not return anything usable for anything. X E.

#

In 3d that would be perpendicular projection. X E.

carmine sigil
#

You can use it to build Euler angles in any number of dimensions

#

Combined with projections

fossil ember
#

Well, 2d angles in 4d?

#

I also wanted to eliminate x, y, and t. X E.

#

Thanks. X E.

carmine sigil
#

We use 2d angles in 3d all of the time, why do you think they wouldn't be useful for 4d as well?

#

Like I really don't understand why you think this

fossil ember
#

They could be, or not. X E.

#

I have tried it before. X E.

carmine sigil
#

So, you decided that, because you couldn't figure out how to use them immediately, they must be useless?

fossil ember
#

No. X E.

carmine sigil
#

Ok, that tracks actually.

fossil ember
#

Anyway, how do you suggest?

#

Like find a moving dimension, use it with another, depending which comes out not zero, relate it to others and continue so that like origin is 1, other is unit and compare the totals?

carmine sigil
#

Depends on what you are trying to do, which isn't super clear to me. It sounds almost as if you are attempting to find a direction in 4d space, which would be an element of S^3, which can be specified in a number of different ways, but one way is by using a 4d analogue of Euler angles, and to determine these you can use projections and dot products against basis vectors to find the angles

#

And a big part of that is the identity I mentioned earlier.

fossil ember
#

The identity you used earlier does not work unless I used it wrong. X E.

carmine sigil
#

Then you used it wrong? What can I say, the identity is a proven mathematical theorem

fossil ember
#

In 3d?

carmine sigil
#

In any finite d

fossil ember
#

Okay, then using it wrong. X E.

#

Can you state what cosine equals again so I can try again?

scarlet solstice
fossil ember
#

Javascript. X E.

#

The vector cosine definition is not working. X E.

#

Maybe cosine is not enough?

#

Or perhaps it gets overloaded?

#

Or perhaps I am just using it wrong. X E.

#

Anyway regardless that cosine is not useful to me. X E.

#

Should I resort to my cosine and sine thing to get relative movement to one way?

#

I am dumb right?

carmine sigil
fossil ember
#

So (a.b)/(|a||b|)=cos(angle)?

#

Yeah, still not getting anything from it. X E.

carmine sigil
#

@fossil ember

"I have these two vectors, A, B, and I'm attempting to find the cosine of the angle between them. I am getting X, but I expected Y."

Can you tell me what A, B, X, and Y are here?

fossil ember
#

function cosine(a,b,c) {
//X E
return (dot(minus(a,b),minus(c,b)))/(distance(b,c)*distance(b,a));
//X E
}
//X E
a-b is A, b-c is B, expected something relating to the projection in the program represented by s, but nothing gets it. X E.

#

-156=x, 1.something=y. X E.

#

The program above is enough. X E.

#

Any more you want?

#

Probably a normal and perpendicular issue. X E.

#

Thanks for talking anyway. X E.

#

Well, I guess this is going nowhere. X E.

#

Did not even get much of an answer what to study. X E.

scarlet solstice
fossil ember
#

Thanks. X E.

carmine sigil
fossil ember
#

Getting vectors from them. X E.

carmine sigil
#

Have you tested the minus and distance functions separately to ensure they are giving the results as you expect?

#

As well as dot

fossil ember
#

Seems correct programmatically, they seem to work. X E.

#

I would say yes. X E.

carmine sigil
#

Why do you have the distance function counting down instead of up?

fossil ember
#

Does not matter order, -squared=+square. X E.

carmine sigil
#

The iteration direction.

#

You have it starting from the end of the vector and walking back to the beginning, which is opposite of the way it is both normally done and the way it was done in the other functions

fossil ember
#

-98.60061513425832=X 24.008384767096388=Y. X E.

#

sum of all of them like that does not matter. X E.

carmine sigil
#

The cosine of any angle should be between -1 and 1.

#

So if you're expecting 24 then why?

fossil ember
#

Yeah, multiplying by a distance. X E.

#

Trying to get a total. X E.

#

Probably me being dumb?

#

console.log(point,x,proj,cosine(point,x,proj)*distance(point,proj),setx); X E.

#

Thanks for scrutinizing. X E.

carmine sigil
#

I cannot test your code, because I am currently at a Christmas party. I will test it when I get home

#

Can you test the following just for sanity:

distance([0,0,0,0], [1,1,1,1])

fossil ember
#

Merry Christmas buddy. X E.

carmine sigil
#

Should be 2.

fossil ember
#

Yes, 2. X E.

carmine sigil
#

So if you do cosine([1, 0, 0, 0], [0,0,0,0], [1, 1, 0, 0]) do you get sqrt(2)/2 ?

#

About 0.707

fossil ember
#

Yes. X E.

carmine sigil
#

If you run cosine([2,3,4,5], [0,0,0,0], [3,4,5,6]) do you get 34/(3 sqrt(129))≈0.997844 ?

fossil ember
#

Yes. X E.

carmine sigil
#

If you run cosine([5,3,5,7], [3,0,1,2], [6, 4, 6, 8]) do you get the same answer?

fossil ember
#

Yes. X E.

carmine sigil
#

If you run cosine([5,3,5,7], [3,0,1,2], [6, -4, 6, 8]) do you get 22/(3 sqrt(129))≈0.645664?

fossil ember
#

Yes. X E.

carmine sigil
#

If yes, then your function is working near as I can tell, and I'm not entirely sure what has led you to believe it is not

fossil ember
#

It has no relation to the s, setx, or sety seemingly. X E.

carmine sigil
#

I need more context here

#

What are s, setx, and sety?

fossil ember
#

setx and sety are x and y on plane and s is scaling out from a point to the end point. X E.

#

Clear enough yet?

carmine sigil
#

Not at all

fossil ember
#

Okay, so basically on plane x and y, then s is multiply a line from P to that by it to get end. X E.

#

Still unclear?

carmine sigil
#

Define "plane x", "plane y", "s", "P", "that", "it", and "end", please.

#

I'm guessing s is the name of a function

fossil ember
#

Plane x as in from plane center, multiply an x vector from that and add it, same for plane y, s is like 4d z, P as in the original equation pinned, "it" as the point on plane from x and y defined, and end being like right side, the end point. X E.

carmine sigil
#

Two points is not enough to define a plane uniquely.

fossil ember
#

I have two vectors and a center point. X E.

#

That makes 3 buddy. X E.

carmine sigil
#

Center point meaning the origin?

fossil ember
#

Just make up a point. X E.

#

add 1 in a dimension and 1 in another dimension, boom, x and y vectors. X E.

carmine sigil
fossil ember
#

Yes. X E.

#

They may be not perpendicular. X E.

carmine sigil
#

So you are attempting to find the angle between x and y?

fossil ember
#

No. X E.

#

Finding what originally the x,y, and s were. X E.

#

Or in the original equation, t. X E.

carmine sigil
#

s being the "center" point of this plane?

fossil ember
carmine sigil
#

I'm sorry I don't really understand what it is you are attempting to accomplish.

fossil ember
#

4d+ projection and viewing. X E.

#

Also simplifying the equation some. X E.

#

shrimplify. X E.

carmine sigil
#

Ok, I'm reading your OP, and I don't understand what that equation is meant to represent or how you arrived at this, but given that you are clearly attempting to create a visualization of 4d space, have you looked at prior art?

fossil ember
#

Yes. X E.

carmine sigil
#

For instance, code golf did an entire series on his 4d engine for 4d golf, and it's open source.

fossil ember
#

It can't do 6d. X E.

#

CodeParade*. X E.

carmine sigil
fossil ember
#

Not far off, 4d golf. X E.

carmine sigil
#

And there is a difference between it doesn't support 6d and it can't be extended to 6d

fossil ember
carmine sigil
#

I'm not sure what you mean here by "native."

fossil ember
#

If it gets too late for you feel free to go. X E.

fossil ember
#

And native to more dimensions, not necessarily same math in 5d as 6d. X E.

carmine sigil
#

The entire discipline of linear algebra was developed to handle arbitrary dimensions, it is the same math

fossil ember
#

We shall see what works and what doesn't. X E.

carmine sigil
#

Well. Best of luck.

fossil ember
#

What would you suggest asking tomorrow?

carmine sigil
fossil ember
#

From what I heard CodeParade uses matrices too. X E.

fossil ember
carmine sigil
#

???

fossil ember
#

Thanks, I know the maker. X E.

fossil ember
#

Check out Godot ND by same person. X E.

carmine sigil
#

Instead, I'm going to go afk. Have a good evening.

fossil ember
#

Okay, so other people, how to solve the original and what is x and y and t?

midnight plankBOT
#

@fossil ember Has your question been resolved?

fossil ember
#

I just found out 4d golf is also a different type of 4d+ maybe. X E.

#

<@&286206848099549185>, I am doomed right?

obtuse mason
#

Yep

fossil ember
#

Well, how should I solve?

fossil ember
#

Hello bots. X E.

#

Who posted?

fossil ember
#

Also, if I can solve, what would be the way to define boundaries of the solution?

midnight plankBOT
#

@fossil ember Has your question been resolved?

#
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#
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lament fox
midnight plankBOT
latent wadi
lament fox
#

i think the closed sets are sets that contain all the non-open subsets of Q and ofc emptyset

#

so its not hard to see that the space is conneccted because a set cant be open and closed other than empty and entire space

#

but im not sure how to do part iii

fallow palm
#

what is this X E. thing?

lament fox
fallow palm
woeful jetty
#

hi does anybody understand U substitution bc i CANNOT understand ts 😭

midnight plankBOT
#

@lament fox Has your question been resolved?

midnight plankBOT
#
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midnight plankBOT
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vapid jacinth
#

How would I answer this question without manually calculating for 90, 91, 92, ..., 100 and adding them all up? Calculators are allowed but not those features where you just plug in the parameters.

vapid jacinth
#

Is there some sort of formula for this?

cerulean oyster
#

Binomial to Normal approximation

#

or a calculator

vapid jacinth
#

How do I do that?

cerulean oyster
#

Do you already know what normal distribution is?

topaz epoch
vapid jacinth
vapid jacinth
#

I think only the 83 and 85 are allowed.

cerulean oyster
#

The fact that it says "poor performance" makes me suspect that you are not really supposed to pull off all the calculations as Bin.dist

vapid jacinth
#

Ah so something like that most likely won't come up in the exam.

cerulean oyster
#

If it happens and you still didnt learn about bin -> normal approximation

vapid jacinth
#

Because I recall the lecturer didn't really calculate it, he just kinda went over it.

cerulean oyster
#

then you will then just have to crunch up a lot of numbers

vapid jacinth
#

I see.

#

Alright then thank you.

#

.close

midnight plankBOT
#
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midnight plankBOT
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jade magnet
#

wait so this is about circle theorems but

midnight plankBOT
jade magnet
#

how do i prove that an angle BAC never changes

umbral timber
#

!xy

midnight plankBOT
#

Please show the original problem, exactly as it was stated to you, with the entire original context. A picture or screenshot is best. If the original problem is not in English, then post it anyway! The additional context might still be helpful. Do your best to provide a translation.

jade magnet
#

no matter where A is placed on the circle

jade magnet
latent wadi
jade magnet
jade magnet
#

could you refresh my memory on that

lyric charm
jade magnet
#

i heard of it but might have forgot it

jade magnet
latent wadi
lyric charm
#

cause rn even if we fix B and C then the size of angle A isn't independent of its placement on the circle

#

!xy

midnight plankBOT
#

Please show the original problem, exactly as it was stated to you, with the entire original context. A picture or screenshot is best. If the original problem is not in English, then post it anyway! The additional context might still be helpful. Do your best to provide a translation.

jade magnet
#

surely the size wont change as long as a doesnt cross the chord BC

#

if that makes sense

latent wadi
#

Yeah something like that

jade magnet
#

yeah thats what i meant

#

mb

#

should have made that clear

#

but yeah

latent wadi
#

You might wanna search up "inscribed angle theorem"

#

And also search up its derivation, which is pretty basic

#

Or if you really want to, you can wait for a helper to come here and explain it to you

jade magnet
#

or at least it looks something like that

#

hold on im trying to understand

latent wadi
jade magnet
#

wait so is only the red part inscribed or are the blue parts inscribed too

#

not "parts" sorry

#

angles but angle when i say angle

#

surely it's dependant on the point they lie in?

#

idk no lie in isnt the right wor

#

word

latent wadi
#

What website are you reading

jade magnet
#

how do i say an angle is in specific points

latent wadi
jade magnet
#

from here

latent wadi
#

I think you should just search up "what is the inscribed angle theorem"

latent wadi
jade magnet
timber sequoia
#

take 2 points on the circumference of a circle

#

connect those to the center of the circle to make a triangle

jade magnet
#

oh ok

timber sequoia
#

now connect the same two points to the other side on the circumference of the circle

jade magnet
timber sequoia
#

the inscribed angle theorem states that the angle made by the triangle at the center is double of the angle made at the circumference.

jade magnet
#

so angles on both the red circled and blue circled points are inscribed

#

ok

jade magnet
#

i remember that

#

ok so the central angle is double the size of the inscribed angle

#

am i right to say this

timber sequoia
#

any ideas to solve the question then?

#

yes

jade magnet
#

am i correct to say that BDC is the central angle?

#

and if it's bdc would that imply the angle is 0 or 180

timber sequoia
#

is BC a chord or the diameter?

jade magnet
#

wait

#

is it supposed to be the diameter

#

is that a requirement

timber sequoia
#

you haven't given the question so I was asking

#

it's not a requirement

#

well if you want BDC to be the central angle then yes

jade magnet
#

for the inscribed angle theorem or the inscribed angle A being the same

#

idk what theorem you call the right one

#

but yeah

jade magnet
#

well if the central angle doesnt change

#

does this imply the angle BAC is always equal to 180/2

#

which is 90 degrees

#

but wait

#

surely in my example

timber sequoia
#

if BC is the diameter and D is the midpoint yes.

jade magnet
#

it isn't 90 degrees

jade magnet
#

what if bc isnt the diameter

#

how do i still prove it

timber sequoia
#

it's doesn't change much

#

given BC is a chord, how would you form a central angle?

jade magnet
#

congruent triangle?

#

similar triangle?

#

dont remember what exactly you call it but something like that

timber sequoia
#

just a 'triangle' is fine

#

it would be isosceles, though, if you're concerned

jade magnet
#

if we can move point A wherever so long as

timber sequoia
#

it doesn't have to be

jade magnet
#

its not below the chord BC

timber sequoia
#

sorry it won't be isoceles

#

I'm dumb

#

it'll just be a triangle

jade magnet
#

oh ok its fine

jade magnet
#

why would it work for the triangle we're looking at

#

we proved it for a "different case" in my eyes

#

which doesnt feel right

timber sequoia
#

can you elaborate?

jade magnet
#

i get it now

#

you add a point to the centre of the circle

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lets call it D this time

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and then we know from the inscribed angle theorem that if BC was the diameter aka the vectors BD and BC has the same direction

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then BAC must always be 90 degrees on that case

timber sequoia
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no no

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the diameter simply means the chord is cutting through the center

timber sequoia
jade magnet
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but what i am saying is if its true for the diameter

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it must be true for a non-diameter chord as well

timber sequoia
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you could take it that way sure

jade magnet
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so long as the angle BDC doesnt change

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then BAC cant change

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oh ok

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i just overcomplicated it

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basically yeah

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"if BDC doesnt change BAC also cant change"

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i understand now

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but then the next thing to ask would be

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how do we prove the inscribed angle theorem

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because we did this all "assuming" the inscribed angle theorem is true

timber sequoia
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there's a simple proof you can get just by searching but I can try to explain if you wish

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here's a nice one

midnight plankBOT
#

@jade magnet Has your question been resolved?

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jade magnet
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wait a second

midnight plankBOT
jade magnet
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what if you had this

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surely you cant use the inscribed angle theorem this time

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oh wait

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is the inscribed angle theorem still true

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is the reflex angle BOC still double BAC

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nvm

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its fine

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for a second i felt it wouldnt be true

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but it still would be

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.solved

midnight plankBOT
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thorny folio
#

Hello great math fellows, here I am with another question(sorry).
So it's regarding inner product spaces.
Let say we have two inner product space <,>, and [,] on a linear space V. Assuming both satisfy all required axioms to be an inner product space of course.
I'm asking if is it possible that <,> inner product space has some extra porperties which [,] lacks? or viceversa? I mean some dedicated properties regarding an inner product space.
And if yes, giving some examples would be apprectiated.

midnight plankBOT
#

@thorny folio Has your question been resolved?

midnight plankBOT
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@thorny folio Has your question been resolved?

fossil ember
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Just to be clear, no need to be sorry about having questions, you learn, I am happy for you and others. X E.

fossil ember
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Good luck solving. X E.

midnight plankBOT
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@thorny folio Has your question been resolved?

thorny folio
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So it seems it's not really possible. IDK. I tried some trial and error and playing around if I'm able to find anything. But seems the axioms are so strict that it's almost restricted us completely. IDK.
Math bless us all

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.close

midnight plankBOT
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midnight plankBOT
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buoyant fjord
midnight plankBOT
buoyant fjord
#

Let $e \in E$. Let $D={d(e,x) \mid x\in E, x \neq e}$. Since $D \subset \mathbb{R}$ and $0$ is a lower bound of $D$, $\inf(D)$ exists. Assume, for sake of contradiction, $\inf(D)=0$.

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oh

grand pondBOT
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Julian

buoyant fjord
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Assuming $\inf(D)=0$ leads to us being able to show $\lim_n p_n=e$ possibly?

grand pondBOT
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Julian

buoyant fjord
buoyant fjord
brave gorge
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Did you try it

buoyant fjord
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i was trying to figure it out

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i think

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at the very least we can get a subsequence

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that converges to e

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which already provides the contradiction because we cant have subsequences of $p_n$ converging to $e$ since $l \notin E$

grand pondBOT
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Julian

lavish venture
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how does this in any way answer the question?

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are you saying D is an open cover of E?

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not sure what you’re trying to get at here

buoyant fjord
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no

lavish venture
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what are you doing then?

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is there another question you’re answering or something?

buoyant fjord
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if the infimum isnt 0

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that means we can do the union of the sets of the infimum(D)/2 neighborhood of every point in E

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neighborhoods are all disjoint then

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@lavish venture

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infimum /2

lavish venture
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ok and why doesn’t that have a finite subcover?

brave gorge
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I don’t really understand the construction at all to be honest

buoyant fjord
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because E is infinite so we can construct a bijection

lavish venture
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can’t it be that all the other points are within inf(D) of each other but farther than inf(D) from e?

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like you fixed e

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and this inf distance only applies for distances of points relative to e

buoyant fjord
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oh shoot

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i deleted an important part

lavish venture
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like let’s say we’re on the real line and i have a cluster of points around 1 and let’s take e to be 2 or something and for the sake of argument say the closest point is x = 1.01

buoyant fjord
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it should be inf of distances of arbitrary nonidentical points of E

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and then

lavish venture
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and then

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not sure what you mean though

buoyant fjord
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oh yeah that makes no sense

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oh wait

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we need a different radius for each neighborhood

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sorry im like brain farting

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uh

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we can do inf of

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for each point

brave gorge
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Assuming ftsoc that inf(D) is zero wont really do anything

buoyant fjord
grand pondBOT
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Julian

buoyant fjord
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and then

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we can use inf/2 for the neighborhood of that e

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and thats how we get the cover

lavish venture
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yes that makes more sense

buoyant fjord
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did i fix it or am i still being dumb

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ok good

lavish venture
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and it’s important that l isn’t in the sequence or else the inf would be zero

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and you wouldn’t cover that point

buoyant fjord
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yeah cuz

lavish venture
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the inf can’t be zero because the limit is unique and l isn’t in E

brave gorge
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Yup

lavish venture
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only one cluster point

buoyant fjord
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oh yeah i got it i think

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thanks guys

lavish venture
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it’s important you don’t use one particular inf uniformly though

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as you just fixed

buoyant fjord
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yeah

brave gorge
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The broader point is that any covering such that each open set in the cover only captures a finite number of points will work

buoyant fjord
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for some reason i like disjoint ones

lavish venture
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easier to construct

brave gorge
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I think yours is the most natural one

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Yup

buoyant fjord
lavish venture
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since p_n is arbitrary

lavish venture
buoyant fjord
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ok adios amigos

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.close

midnight plankBOT
#
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midnight plankBOT
#
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lusty python
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How do I solve for $(m, n) \in \mathbb R^2$?

$8n^2 + m^2 + 8mn - 24n + 4 = 0$

grand pondBOT
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1 divided by 0 equals Infinity

lusty python
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original question

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find $(m, n) \in \mathbb R^2$ such that the equation above has roots $x_1 = x_2$

grand pondBOT
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1 divided by 0 equals Infinity

lusty python
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I started out by working out $\Delta$ for this, which is $8n^2 + m^2 + 8mn - 24n + 4$

grand pondBOT
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1 divided by 0 equals Infinity

next bobcat
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Ok

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so the discriminant is found

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and for it to have equal roots, it must be 0

next bobcat
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@lusty python you here?

lusty python
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im here

next bobcat
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so first you must find $b^2 - 4ac$

grand pondBOT
next bobcat
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did you do that

lusty python
grand pondBOT
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1 divided by 0 equals Infinity

lusty python
next bobcat
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you sure

lusty python
grand pondBOT
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1 divided by 0 equals Infinity

next bobcat
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oh ok

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just retry it because methinks it’s a different value

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and then try to equate it to 0

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that’s pretty much it

vivid yoke
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,w simplify 4(n+1)^2 -4(2n(2-m)-m^2-n^2)

twilit jetty
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no spoilers

lusty python
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different value

vivid yoke
lusty python
twilit jetty
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this is correct

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now you need to find out when this = 0, to do that you can first divide both sides by 4 for extra convenience

twilit jetty
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then from there, theres a few ways you can go about this

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think about trying to find or form perfect squares

lusty python
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yeah

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i can see what i can do now

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ty

twilit jetty
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if you dont know where to go from here, I can tell you what is essentially the answer to what the perfect squares are

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np

lusty python
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i got to the sum of 2 perfect squares = 0

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ty

twilit jetty
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alr, which ones

lusty python
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$(m + n)^2 + (n - 1)^2 = 0$

grand pondBOT
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1 divided by 0 equals Infinity