#help-49
1 messages · Page 266 of 1
oh yeah
that sequence converging to 0 for any (x_n) for your specific problem and what i said here are very related
wait one sec im trying something
why are you using two sequences?
because the slope of that secant line is the value (f(b) - f(a))/(b-a)
and that value converge to 0 when you take b values close to -2
an N such that for all n>N $d(x_n,-2)<d(x,-2)/2$ maybe lemme try it
Julian
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?
yeah cuz
ok now i’m going to tell you that it’s very easy to adjust that proof to apply to your problem too
because…
when you take an irrational point, the secant line expression is 0
yeah
yeah it's not a product, it's cases
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
i thought the irrational case was trivial right
yes
yes but you still have to state it
i am yea
i mean if you're doing a proof
i will include it
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
im not doing 2
im doing an arbitrary mixed one]
what is a mixed sequence?
like with irrational and rational
btw this can be shown with a pretty simple limit computation. are you allowed to do that or do you really need to do epsilon delta stuff?
do you mean that a_n and b_n are subsequences?
probably
no
no its the fact that the difference quotient is 0
for irrationals
so thats less than whatever epsilon
oh do you mean
3(x_n+2)^2's limit?
cuz the division
(x_n) is an arbitrary sequence converging to a. and (f(x_n)- f(a))/(x_n-a) can be viewed as a sequence
shouldn't it converge to -2?
it does but the difference quotient converges to 0 is what we wanna show
(x_n) does by assumption
the long one here should converge to 0
you said it converges to a
well a is -2 i think
oh yeah
what is b?
wheres b
^
oh
oh i can prob just assume the limit cuz we had this on an older homework
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
since the quotient is 0 when x_n is irrational
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great
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Renato
where is your question
can someone explain what does this mean?
there's several different points that could demand explanation
i just find it confusing
can you at least narrow down to which of the 4 paragraphs you want explained from this picture?
that or we could do it the painful way and i could extract this info from you like up to 4 rotten teeth
@tidal turret
i think second paragraph is kind of confusing
paragraph 2 is an intuitive explanation of WOP
it gets fuzzy when it talks about n0
it says:
if A is infinite, pick whatever element you want from there, and consider only the elements of A that are leq that one
can we narrow it down to a down to earth example test case?
sure
suppose A is the set of all primes
it's infinite, so big
yes
but. 67 is in A
so we can narrow down to the finite set {primes <= 67} and the minimum won't change
we could have also took the first prime from the set of all primes
2
sure we could
we have freedom of choice here
i am just giving an example
okay let's try 67 and then 2 please
sure i think
you want this worked out formally?
it will be very boring and not remotely enlightening
not really no. im not in that stage of my career
ok then let's not
this is an intro to wop
the part about the intersection it gets fuzzy
and consider only the elements of A that are leq that one
i translated it into plain English
i see
is tricky to follow
why they say consider finite then consider infinite set
finite sets are more straightforward
with a finite set we can think about "iterating" over all its elements and it'll come to an end
because. well that's the entire thing with finite sets isn't it
@tidal turret Has your question been resolved?
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,rccw
hold on nvm
blue, yellow, and green are only adjacent for (528,529) (1495,1496)
so except them, each blue, each yellow, and each green contributes 2 pairs
so (floor(2023/23)+floor(2023/88)-floor(2023/(23×88))×2
-2 for overcounting
yeah thats what i thought
but this gets 2(87+22-0)-2=216
anywhere i went wrong?
hmm if yes I dont see where
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Hi, I needed help with set cardinalities to solve a coding problem (specifically advent of code 2025 day 5 part 2)
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
1 divided by 0 equals Infinity
...
i wanted a general formula for this
without having to do a lot of code
well you probably gotta use a sort and merge algorithm
?
like, sort all the intervals based on their starting integer, iterate through them and merge if they overlap or touch
what if they are disjointed?
that's the problem
well since it is sorted if they don't overlap the next one is going to be a new separate interval
idk if thats sarcasm or not but ok
Do they share any integer?
can you elaborate on that please?
If you had any probability class this should sound awfully similar
but if they are independent (dont share any integer), then the cardinality of that set is the sum of the cardinalities
they may share any integer
Okay, then you probably want a hash map here
sadly you will have to iterate through all the arrays
oh i tried that
maximum limit is around 15 digits
so that won't help
as to cardinality of individual sets?
#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
wrong answer
as to the maximum end value
we dont really care about the values really
just about their multiplicity (how many times they appear)
Oh goddam i didnt read this is an interval not an array
yeah no clue
like, from the theory side, you can do the sum of all the intervals - the sum of all their intersections
but thats O(n^2)
Think hard
isn't it an interval
not even n^2, its n!, lmao.
Yeah you would want to be looking for an algorithm
Main idea is basically a sweep-line-like algorithm
Alr
How does it work?
You can also start from how you sorted your intervals
And consider the subproblem of "how many elements in the union of first k intervals
Dp question eh?
I was thinking of that approach
Got 2 base cases
And don't know how to move on
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.
hmm... possible, takes n log n time iirc. This is not a sweepline-like algorithm
ill draw a thing rq just to check cause im doubting myself
Take your time
I know of an approach which goes along those lines which uses an ordered-set data structure
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
na i was wrong
So is it the same as this?
A union of intervals can be written as a union of disjoint intervals
Same way of sorting, different processing afterwards
Kk
yeah, union of previous intervals is just a loss of information
Sorting them out and using the end-start values is prob best
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gl
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i need help in understanding the answer of this question
Do you remember what a closed circle (filled in) vs open circle represents)
yes a closed circle is equal to f(x), and the open circle is excluded from the function
Right
If we start with the 2nd question which is simpler
What does the question ask for?
f of -2
Yeah
but idk what answer to put
Is that what you circled?
Are you sure? Look at the x-value
its the other one right
Yeah,
so how do i look for the answer?
So think about what a fuller circle means vs a non filled circle
i put the closed circle? correct
Yeah exactly
and what value is the closed circle? it doesn't indicate in the image
It does say
You can count the y-direction
The vertical axis
In the same way you counted x=-2 is two blocks to the left
Apply the same concept to the y axis
Did you get an answer?
Not exactly. count again
And you should start from the point where the two axes intersect
is it a negative on the y axis?
It is negative!
-2?
Exactly
it's looking for the value or limit if x is -2 to the left
am i right?
Yeah, so as x approaches -2 from LEFT to RIGHT, what does the value of x reach?
In the same way, if it said -2^(+) it would mean the value as x approaches -2 from RIGHT to LEFT
wouldn't - mean to the left? or is it the other way around?
Other way around
ohh so it would be to the right?
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)
ohhh
makes sense
And if we have a positive sign, we start from the positive and move in the opposite direction so towards the negatives
This is a good thumb rule to remember
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
Yup
ohh nice
One important thing: make sure you follow the graphs line
how would i know
Look at the graph
You’re going the wrong way now
You want to start in the bottom left corner
And follow the graph to the right
until we reach -2?
Yeah
okay so we would stop here?
You’d stop here
and then we get the value of the closed circle?
Exactly
Yup
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hey i dont think i understand the difference between prims and nearest neighbour
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
but i dont even know which algorithm that is
i dont understand the differences can somebody help
nvm
my teacher explained it
.solved
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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.
What have you tried
The answer is $\frac{\binom{28}{5}}{\binom{35}{6}} \cdot \frac{35}{6}$
Poly(^///^)
But I don't get where the 35/6 come from
Oh
Mb
Probability
Sorry bruh the question was asked yesterday so I didn't remember it correctly
But everything else is right
so the question is what’s the probability 6 people picked at random are all not sitting next to each other?
Are there a different between choosing 6 people from 35 people in a circular table and just choosing 6 from 35?
Yes
what would “just choosing 6 from 35” mean?
it would be different if they were e.g. in a line
$\binom{35}{6}$ by that I mean is the the sample space?
Poly(^///^)
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
Yeah that's why I asked and that what I did
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
But where the 35 come from
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
there are 35 seats you can choose to fix the first person at
So the sample space is binom{35}{6}/35?
it depends you how do the problem really
So like, is that the fixed person make the difference ? that's why I asked this question
hmm
but yes this is a fair thing to say
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
How can I do the problem with the sample space binom{35}{6}?
Like what's the thought process for it
if you imagine the tables as not being the same under rotations, so that there are 35 choose 6 tables, then you can get the “good ones” by first choosing one of the 6 people and of the 35 seats to assign them
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
with this interpretation there isn’t really a “choosing a first seat”
do you know what i mean by “same under rotations”?
I'm trying to wrap my head around it, It's just that I can't imagine the difference between linear and circular case

the difference is not between linear and circular here

doesn't the rotation make them different?
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
also generally in school it’s expected for you to treat tables that are the same up to rotation as the same
you are not
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?
ngl I'm not sure what you said here
it will be the exact same except there are 35 ways to pick which seat to put the first person at, so that’s where the *35 will come in
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
do you mean in the tables are the same under rotations interpretation?
because no matter where you put the first person, the table looks the same
when they are the same under rotations
so there’s only one table
not 35 different ones you could make with one person
Okay tbh I'm not sure what you're taking about really
😭
did you understand this?
No I meant
these
I get that
that*
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?
yeah
now let’s say we consider them different
i can put the first person at any of the 35 seats and those tables will all be distinct
okay
so that’s why the placement of the first person matters in one case but not the other
but shouldn't they be different? I meant the assumptions are different
what’s they
"consider tables that are the same under rotation the same " and "consider them different"
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
Okay so in 35*(28 choose 5)/6
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
(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
No I meant if we're counting different for sample space so do the event
yes that is right
i get that...
that’s why the 35 gets corrected for both in the total and in the good events
But I've thought you said smth different 😭
Okay clearly I'm wasting your time bruh
Thanks for the help
It does for me haha
Well it used to
Okay Imma close the channel
Have a nice day!!
.close
Closed by @slate crater
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cya
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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?
@lethal aurora Has your question been resolved?
@lethal aurora Has your question been resolved?
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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.
dunno where to start
its the ratio of the radii
because of the formula pi * r for the perimeter of a half circle
ik r_1 is 1000 but idk r_2
3 lanes 14 feet
so add them?
multiply
,calc 1000143
Result:
42000
like this? 
Add the lanes, multiply with the ratio
no like 1000 + 3 * 14
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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.
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.
linear programming
Any more wisdom?
Well I know linear programming can but efficient algorithms?
@fossil ember Has your question been resolved?
Trying for O(n), not O(n^(n^2)). X E.
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
Maybe, or number of equations. X E.
Okay, n^2?
I don't want the second option I mentioned. X E.
.
So O(?)?
Estimate?
Well, any good books on linear programming?
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?
No. X E.
There is officially no recommended book yet. X E.
How is this the bottom help already?
Am I doomed?
linear programming is usually beyond lower division undergrad math knowledge
you can also try #optimization
Well I do Calculus before done with Precalculus in school so why not?
good for you
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.
I'm not sure I understand your meaning here? How is it trash?
Is this #optimization or #game-theory ?
It returns values not useful for finding one way from another, it does not work for practically anything etc. X E.
I have tried the lin alg version and distances. X E.
You already need two values to specify a direction in 3d, you just need 3 to specify a direction in 4d.
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.
You can use it to build Euler angles in any number of dimensions
Combined with projections
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
So, you decided that, because you couldn't figure out how to use them immediately, they must be useless?
No. X E.
Ok, that tracks actually.
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?
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.
The identity you used earlier does not work unless I used it wrong. X E.
Then you used it wrong? What can I say, the identity is a proven mathematical theorem
In 3d?
In any finite d
Okay, then using it wrong. X E.
Can you state what cosine equals again so I can try again?
I don't think you should be so proud of that tbh, because it seems you are still lacking a lot of the basics. There's a reason we usually learn things in order
Yes. X E.
Alright, what was that cosine again?
How is this wrong, it is obviously wrong. X E.
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?
a.b = |a| |b| cos θ (assuming the L2 norm)
@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?
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.
I think Omni wanted an example with actual numbers, not just more variables. So something like, I ran cosine(1, 2, 3) and expected 0.222, but got 0.555
The number set is random and 10d or more, I could give a program though. X E.
Thanks. X E.
Is a, b, and c here vectors of numbers, if so, is b the center of the angle, so you are finding angle abc considered as points?
I am using points yes. X E.
Getting vectors from them. X E.
Have you tested the minus and distance functions separately to ensure they are giving the results as you expect?
As well as dot
Why do you have the distance function counting down instead of up?
Does not matter order, -squared=+square. X E.
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
-98.60061513425832=X 24.008384767096388=Y. X E.
sum of all of them like that does not matter. X E.
The cosine of any angle should be between -1 and 1.
So if you're expecting 24 then why?
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.
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])
Merry Christmas buddy. X E.
Should be 2.
Yes, 2. X E.
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
Yes. X E.
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 ?
Yes. X E.
If you run cosine([5,3,5,7], [3,0,1,2], [6, 4, 6, 8]) do you get the same answer?
Yes. X E.
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?
Yes. X E.
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
It has no relation to the s, setx, or sety seemingly. X E.
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?
Not at all
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?
Define "plane x", "plane y", "s", "P", "that", "it", and "end", please.
I'm guessing s is the name of a function
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.
Two points is not enough to define a plane uniquely.
Center point meaning the origin?
Just make up a point. X E.
add 1 in a dimension and 1 in another dimension, boom, x and y vectors. X E.
So x and y are defined as vectors from some point. So if this point is [1,2,3,4] and x is [0,1,0,1] then from the origin the head of x is at [1,3,3,5]?
So you are attempting to find the angle between x and y?
No. X E.
Finding what originally the x,y, and s were. X E.
Or in the original equation, t. X E.
s being the "center" point of this plane?
No, on a line from a P point to the plane, make its magnitude times s. X E.
I'm sorry I don't really understand what it is you are attempting to accomplish.
4d+ projection and viewing. X E.
Also simplifying the equation some. X E.
shrimplify. X E.
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?
Yes. X E.
For instance, code golf did an entire series on his 4d engine for 4d golf, and it's open source.
Sorry code parade
Not far off, 4d golf. X E.
And there is a difference between it doesn't support 6d and it can't be extended to 6d
True but may as well go native. X E.
I'm not sure what you mean here by "native."
If it gets too late for you feel free to go. X E.
His is for Unity, I am using Godot and Rust. X E.
And native to more dimensions, not necessarily same math in 5d as 6d. X E.
The entire discipline of linear algebra was developed to handle arbitrary dimensions, it is the same math
We shall see what works and what doesn't. X E.
Well. Best of luck.
What would you suggest asking tomorrow?
This might help https://github.com/godot-dimensions/godot-4d
From what I heard CodeParade uses matrices too. X E.
Different kind of 4d+. X E.
???
Thanks, I know the maker. X E.
Even the creator acknowledges orthogonal vs normal projection. X E.
Check out Godot ND by same person. X E.
Instead, I'm going to go afk. Have a good evening.
Okay, so other people, how to solve the original and what is x and y and t?
@fossil ember Has your question been resolved?
I just found out 4d golf is also a different type of 4d+ maybe. X E.
<@&286206848099549185>, I am doomed right?
Yep
Well, how should I solve?
Also, if I can solve, what would be the way to define boundaries of the solution?
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What have you tried
part a is straitghforward
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
what is this X E. thing?
what X E
scroll up a bit, some guy was adding X E at the end of all of his messages
here
hi does anybody understand U substitution bc i CANNOT understand ts 😭
that's just a him thing
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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.
Is there some sort of formula for this?
How do I do that?
Do you already know what normal distribution is?
a convenient normal distribution calculator I use is desmos
No I don't.
There's specific guidelines for the type of calculator you can bring in. I got a Casio FX-85 CW.
I think only the 83 and 85 are allowed.
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
Ah so something like that most likely won't come up in the exam.
If it happens and you still didnt learn about bin -> normal approximation
Because I recall the lecturer didn't really calculate it, he just kinda went over it.
then you will then just have to crunch up a lot of numbers
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wait so this is about circle theorems but
how do i prove that an angle BAC never changes
!xy
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.
no matter where A is placed on the circle
sorry it took me a while to put the question up
Do you know the inscribed angle theorem?
i know this is true but i want to know why
uhh
could you refresh my memory on that
you sure about this
i heard of it but might have forgot it
oh yeah mb
Yeah this isnt true
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
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.
surely the size wont change as long as a doesnt cross the chord BC
if that makes sense
Yeah something like that
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
ok so an inscribed angle is any angle that lies on the circumference of a circle?
or at least it looks something like that
hold on im trying to understand
It's an angle with 2 points on the circumference of the circle and the angle at the center of the circle
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
What website are you reading
how do i say an angle is in specific points
Like where are you searching this
How inscribed angles work with step-by-step examples.
✴️Watch https://www.youtube.com/playlist?list=PL_lfD8bObQOdu-s3NePd4S8srxq0HO0cB
0:00 intro
0:12 central angle, inscribed angle, intercepted arc
0:48 how inscribed angles are related to intercepted arcs
1:51 example 1
2:34 example 2
2:54 example 3 - inscribed angle with a diameter
3:56 e...
from here
I think you should just search up "what is the inscribed angle theorem"
Instead of watching this kind of video, which shows how to apply the theorem.
brev i dont even know if i know the correct definition for an inscribed angle
take 2 points on the circumference of a circle
connect those to the center of the circle to make a triangle
oh ok
now connect the same two points to the other side on the circumference of the circle
i just checked and basically an inscribed angle is any angle who's point lies on the circumference
the inscribed angle theorem states that the angle made by the triangle at the center is double of the angle made at the circumference.
yeah
i remember that
ok so the central angle is double the size of the inscribed angle
am i right to say this
well if it's a triangle surely if we added an extra point called d between the chord b and c then
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
is BC a chord or the diameter?
how would that be the diameter
wait
is it supposed to be the diameter
is that a requirement
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
for the inscribed angle theorem or the inscribed angle A being the same
idk what theorem you call the right one
but yeah
ok
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
if BC is the diameter and D is the midpoint yes.
it isn't 90 degrees
ohh ok
what if bc isnt the diameter
how do i still prove it
it's doesn't change much
given BC is a chord, how would you form a central angle?
ohh yeah of course you can just create a uhh what do you call it
congruent triangle?
similar triangle?
dont remember what exactly you call it but something like that
why does it have to be isosceles
if we can move point A wherever so long as
it doesn't have to be
its not below the chord BC
oh ok its fine
but still if it works for another triangle
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
can you elaborate?
what i mean is to form a central angle- oh wait
i get it now
you add a point to the centre of the circle
lets call it D this time
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
then BAC must always be 90 degrees on that case
what you have here is a non-diameter chord
i know
but what i am saying is if its true for the diameter
it must be true for a non-diameter chord as well
you could take it that way sure
but i guess
so long as the angle BDC doesnt change
then BAC cant change
oh ok
i just overcomplicated it
basically yeah
"if BDC doesnt change BAC also cant change"
i understand now
but then the next thing to ask would be
how do we prove the inscribed angle theorem
because we did this all "assuming" the inscribed angle theorem is true
there's a simple proof you can get just by searching but I can try to explain if you wish
here's a nice one
ok let me check
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wait a second
but what if a was on the other side
what if you had this
surely you cant use the inscribed angle theorem this time
oh wait
is the inscribed angle theorem still true
is the reflex angle BOC still double BAC
nvm
its fine
for a second i felt it wouldnt be true
but it still would be
.solved
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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.
@thorny folio Has your question been resolved?
@thorny folio Has your question been resolved?
Just to be clear, no need to be sorry about having questions, you learn, I am happy for you and others. X E.
Much appreciated
Good luck solving. X E.
@thorny folio Has your question been resolved?
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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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, $\inf(D)=0$.
oh
Julian
Assuming $\inf(D)=0$ leads to us being able to show $\lim_n p_n=e$ possibly?
Julian
What’s e?
an arbitrary element in E
right here
Did you try it
i was trying to figure it out
i think
at the very least we can get a subsequence
that converges to e
which already provides the contradiction because we cant have subsequences of $p_n$ converging to $e$ since $l \notin E$
Julian
this doesn’t make any sense
how does this in any way answer the question?
are you saying D is an open cover of E?
not sure what you’re trying to get at here
no
what are you doing then?
is there another question you’re answering or something?
if the infimum isnt 0
that means we can do the union of the sets of the infimum(D)/2 neighborhood of every point in E
neighborhoods are all disjoint then
@lavish venture
infimum /2
ok and why doesn’t that have a finite subcover?
I don’t really understand the construction at all to be honest
because E is infinite so we can construct a bijection
can’t it be that all the other points are within inf(D) of each other but farther than inf(D) from e?
like you fixed e
and this inf distance only applies for distances of points relative to e
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
oh yeah that makes no sense
oh wait
we need a different radius for each neighborhood
sorry im like brain farting
uh
we can do inf of
for each point
Assuming ftsoc that inf(D) is zero wont really do anything
what i meant is for every e in E we take $inf({d(e, x) |x \neq e})$
Julian
and then
we can use inf/2 for the neighborhood of that e
and thats how we get the cover
yes that makes more sense
and it’s important that l isn’t in the sequence or else the inf would be zero
and you wouldn’t cover that point
yeah cuz
the inf can’t be zero because the limit is unique and l isn’t in E
Yup
only one cluster point
it’s important you don’t use one particular inf uniformly though
as you just fixed
yeah
The broader point is that any covering such that each open set in the cover only captures a finite number of points will work
for some reason i like disjoint ones
easier to construct
well i dont have to do much at the end except show the disjointness
since p_n is arbitrary
this is fairly straightforward
yeah triangle inequality
ok adios amigos
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How do I solve for $(m, n) \in \mathbb R^2$?
$8n^2 + m^2 + 8mn - 24n + 4 = 0$
1 divided by 0 equals Infinity
original question
find $(m, n) \in \mathbb R^2$ such that the equation above has roots $x_1 = x_2$
1 divided by 0 equals Infinity
I started out by working out $\Delta$ for this, which is $8n^2 + m^2 + 8mn - 24n + 4$
1 divided by 0 equals Infinity
that’s not the discriminant btw
@lusty python you here?
im here
so first you must find $b^2 - 4ac$
BKB
did you do that
main problem is how do i solve for $m, n$ 😭
1 divided by 0 equals Infinity
it's this boy
you sure
$\Delta = b^2 - 4ac$
1 divided by 0 equals Infinity
oh ok
just retry it because methinks it’s a different value
and then try to equate it to 0
that’s pretty much it
,w simplify 4(n+1)^2 -4(2n(2-m)-m^2-n^2)
your discriminant is incorrect, it should be m^2 + 2n^2 + 2mn - 2n + 1 = 0
no spoilers
different value
Okay...
can you check the discriminant?
this is correct
now you need to find out when this = 0, to do that you can first divide both sides by 4 for extra convenience
That’s what i thought
then from there, theres a few ways you can go about this
think about trying to find or form perfect squares
if you dont know where to go from here, I can tell you what is essentially the answer to what the perfect squares are
np
alr, which ones
$(m + n)^2 + (n - 1)^2 = 0$
1 divided by 0 equals Infinity
