#help-0

1 messages · Page 511 of 1

alpine nacelle
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once the 2b etc are correct, you should get -3 at x = -3 and -21 at x = 3

lilac jolt
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hmmmm

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how do i do item 12?

alpine nacelle
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you need to know polynomial reminder theorem, and understand accurately what is the problem at x = -2

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try to calculate the limit at x = -2 and see the problem, then what you have to do will seem clearer

lilac jolt
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division by zero?

alpine nacelle
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yup, that's the problem

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-2 is a root of x²+x-2

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what is the little detail about the numerator that could make this problem disappear ?

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factor x²+x-2, and try to imagine what you would like to see as a factor in the numerator

lilac jolt
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i cant seem to see an x + 2 on the numerator

alpine nacelle
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well, that's because it depends on b, that's the whole point! you accurately pinpointed the problem

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you would like to choose b such that you can factor a x+2 on the numerator

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the question is, how to find this b

lilac jolt
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yes, idk how

alpine nacelle
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you want to factor numerator by x+2, ie you want x+2 to divide the numerator

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do you know polynomial remainder theorem ?

lilac jolt
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no

alpine nacelle
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if you have a polynomial P(x) that you divide by (x+2), you get P(x) = (x+2)Q(x) + r, where Q(x) is some polynomial we don't care about right now, and r is the remainder

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so when you look at x = -2, you get P(-2) = r

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this video may help you understand the theorem better

lilac jolt
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erm

alpine nacelle
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you want x+2 to divide bx²+15x+b+15
said differently, you want the reminder of bx²+15x+b+15 in the division by x+2 to be 0, right ?
so you know your problem has 2 steps: calculating the remainder, and solving remainder = 0

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this polynomial remainder theorem solves the first step

lilac jolt
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what if i just sub -2 on the numerator

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and then i got 5b - 15

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and solved for b

alpine nacelle
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: )

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b(-2)²+15(-2)+b+15 = 5b-15

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and the remainder has to be 0 for x+2 to divide, that's what dividing means

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so what is b ?

lilac jolt
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3

alpine nacelle
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yup

lilac jolt
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do i subbb?

alpine nacelle
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now you know that b = 3 is the value that make it so you can factor both numerator and denominator by x+2

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which will allow you to calculate the limit after simplification

lilac jolt
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i got -1 after evaluating

alpine nacelle
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num = 3x²+15x+18 = 3(x²+5x+6) = 3(x+2)(x+3)
denom = (x+2)(x-1)
so the quotient is 3(x+3)/(x-1), at x = -2 you get -(-2+3) = -1

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that's correct

lilac jolt
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thank you!!

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is the answer for the bonus item, no?

alpine nacelle
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the answer is no, you can have a limit at a point without being defined at this point

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one well known example of this is sin(x)/x which has a limit of 1 at x = 0, despite not being defined at x = 0

lilac jolt
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thank youu

lone heartBOT
#

@lilac jolt Has your question been resolved?

lone heartBOT
#
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waxen turtle
lone heartBOT
waxen turtle
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Idk how to do 27

marsh hamlet
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What is the graph of sqrt(4-x^2)

waxen turtle
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Idk wat it looks liek

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ohh

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like

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2-x

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isk

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idk

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wait that's not how that works

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IDK

marsh hamlet
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,w plot sqrt(4-x^2)

waxen turtle
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So cool

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does the +3 raise it up

marsh hamlet
waxen turtle
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It's liek all stretched

marsh hamlet
waxen turtle
marsh hamlet
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Trust me, it's a semicircle

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Let me draw something out on desmos

waxen turtle
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Oh wait

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I can split it up

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Fr

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where should I split it

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at 2

marsh hamlet
waxen turtle
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at 3

marsh hamlet
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(Semicircle of radius 2 + square of side length 3)

waxen turtle
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So cool

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TY

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.close

lone heartBOT
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lone heartBOT
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tight mauve
#

Hi, just had a quick question. Is (x-1) not written as (x-1)^2 because it's taken as common factor, just wanted to double check my thinking. Thank you

tight mauve
#

Thank you!

#

.solved

lone heartBOT
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obsidian mango
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Could someone please explain why the sign changed on the left-hand side? And in which cases should I change the sign like this

lone heartBOT
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@obsidian mango Has your question been resolved?

cosmic mortar
#

guys what is the formula to find the volume of a square pyramid using delta

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?

gray isle
obsidian mango
gray isle
#

they factored out -1 from the numerator in the fraction after it

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here its so they can get the result of their goal

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(also looks more aesthetically pleasing without excessive - signs)

obsidian mango
gray isle
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look at the induction hypoteheses

obsidian mango
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Yes

gray isle
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that's why they factored out the -

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so they could get that

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$2 + \frac{(-k-3)}{2^{k+1}} = 2 - \frac{k+3}{2^{k+1}}$

ocean sealBOT
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ℝαμOmeganato5

obsidian mango
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Oh I got you
Thank you very much

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But is there another way to solve it without factoring out the -

gray isle
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not really no

obsidian mango
#

Okay, thanks,
Have a great day 🫡

lone heartBOT
#

@obsidian mango Has your question been resolved?

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scarlet heart
lone heartBOT
scarlet heart
#

can someone show me how to do this? Idk where I went wrong

vale wigeon
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@scarlet heart show what you did and then we can tell you where you messed up

scarlet heart
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still my answer is wrong my teaccher didn't even show where

vale wigeon
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what did you get for R

scarlet heart
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brb btw

vale wigeon
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that's correct

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show how you got alpha and its value then

scarlet heart
scarlet heart
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can u js tell me the right answer

vale wigeon
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no

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!noans

lone heartBOT
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The purpose of this server is to help you learn, not to hand out answers. Do not ask someone to give you the answer directly.

scarlet heart
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okay

vale wigeon
#

if you want your answer validated or checked, you have to post your answer

scarlet heart
#

i use this

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wait a sec

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@vale wigeon if u think Im cheating check my msg history lol this is my assignment finished

vale wigeon
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im adhering to the rules of this server.

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show your work still.

lone heartBOT
#

@scarlet heart Has your question been resolved?

lone heartBOT
#
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scarlet heart
#

@vale wigeon

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i got -36.9

vale wigeon
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.reopen

scarlet heart
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degree

lone heartBOT
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lone heartBOT
vale wigeon
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how did that happen

scarlet heart
vale wigeon
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also you do see that your problem said to round the angle to 2 decimal places, yes?

vale wigeon
scarlet heart
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ok

vale wigeon
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you have not shown your work nor answered my question.

scarlet heart
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4sinx - 3cosx so -3

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??

vale wigeon
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can you show what your expansion for $R \sin(\theta - \alpha)$ is?

ocean sealBOT
scarlet heart
vale wigeon
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ok could be done way better with some brackets

scarlet heart
vale wigeon
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but you see that R cos(alpha) should be 4 and R sin(alpha) should be 3, not -3 yes?

scarlet heart
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need help part 2

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this is problem

vale wigeon
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that is part 3

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do you need help with this or with the real part 2?

scarlet heart
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i skip

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2theta to theta

vale wigeon
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you are becoming harder to understand

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but ok

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you have found, correctly, that 4 sin(θ) - 3 cos(θ) = 5 sin(θ - something).

scarlet heart
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i think i can do

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let me confirm my answer

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don ttell me

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60.5 and 193.3 @vale wigeon

vale wigeon
#

very far off. how did you get these?

scarlet heart
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@vale wigeon idk what wrong

scarlet heart
vale wigeon
#

well, if you want to consider me a liar, then i guess i'll just go away.

scarlet heart
#

ok i got everything right nice

#

.close

lone heartBOT
#
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static wagon
#

with 4(a), why do we multiply the combinations and not add them to get our final result?

static wagon
#

like 12C5 x 8C3 and not 12C5 + 8C3

vale wigeon
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bc you pick 5 men and 3 women

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it's the same reason why a two-digit combination lock has 100 and not 20 combinations

static wagon
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but doesn’t ‘and’ imply like P(A) + P(B) or is that not related here

vale wigeon
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no i think you misunderstand

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think of it this way

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there are 12C5 ways to pick which of the men go

static wagon
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yes

vale wigeon
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but for each of those selections you have to make a selection of which of the women go

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in one of 8C3 ways

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you can think of it with like a tree diagram or something

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or like a combination lock again

static wagon
#

oh because it’s a multi-stage event right?

vale wigeon
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like if you have a 4 digit PIN lock you understand why there are not 40 combinations, yes?

static wagon
#

yes

vale wigeon
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yeah same idea

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call it multi stage or whatever else you want

static wagon
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okay

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then when do we add combinations?

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i think that’s where i struggle

vale wigeon
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if there are m ways to do A and there are n ways to do B and these don't overlap and you have to count the ways to do A or B

static wagon
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cus i thought u multiply independent events

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oh hold on

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i sort of get it now

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could you provide like an example for what you said?

vale wigeon
static wagon
vale wigeon
static wagon
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oops that’s not mutually exclusive

vale wigeon
static wagon
#

that makes more sense now

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then how would the question be rephrased if you have to multiply the combinations?

vale wigeon
static wagon
#

so it’s 13 x 8

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.close

lone heartBOT
#
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static wagon
#

with 5e, why isn’t it 70-1 = 69?

lone heartBOT
alpine sable
#

hi

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MY CHANNEL

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go away beluga

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anyway

static wagon
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bc the amount of combinations of all even is 1 so 70 -1

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mate

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the channel has my username

alpine sable
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oops

lone heartBOT
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@static wagon Has your question been resolved?

serene scarab
#

I don’t understand how they have taken it to be 4

static wagon
#

yea i thought that too

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i think they just got confused or wtvr

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but thanks

#

.close

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copper siren
#

help me here

lone heartBOT
small lance
copper siren
wintry wadi
wintry wadi
# copper siren

then can you solve y and z in terms of x?
because then, we can just plug those into the plane equation and solve it

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alpine sable
lone heartBOT
alpine sable
#

Is this a One Sample Test of Hypothesis?

lone heartBOT
#

@alpine sable Has your question been resolved?

alpine sable
#

<@&286206848099549185>

alpine sable
#

<@&286206848099549185>

wide harness
#

!status

lone heartBOT
#
What step are you on?
1. I don't know where to begin.
2. I have begun but got stuck midway.
3. I got an answer but I was told that it's wrong.
4. I got an answer and would like my work checked.
5. I have a question about someone else's work/solution.
6. I have completed the problem and don't need help anymore. Thank you.
7. None of the above
wide harness
#

Also there are 6 questions, which one is it?

alpine sable
# alpine sable

I would like to ask If this a One Sample Test of Hypothesis.

alpine sable
wide harness
#

It looks like two populations and not one.

alpine sable
wide harness
#

One Sample t-Test doesn't exactly apply to two populations?

alpine sable
#

Hm

wide harness
#

This example is one population.

alpine sable
#

Like this?

wide harness
#

Possibly!

alpine sable
#

Okay!

#

Thank you!

wide harness
#

Also you should look for one more thing.

alpine sable
wide harness
#

It's called Paired t-Test too, if there's something in common between the population.

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With all that said, good luck.

wide harness
#

Hmm not sure. Doesn't look like it mentions Paired t-Test?

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Yes, it does measure on differences so it is possibly that.

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Take my answers with a grain of salt though.

alpine sable
alpine sable
wide harness
#

The best idea you should try is to try the formulas to see if they fit with the variables.

lone heartBOT
#
What step are you on?
1. I don't know where to begin.
2. I have begun but got stuck midway.
3. I got an answer but I was told that it's wrong.
4. I got an answer and would like my work checked.
5. I have a question about someone else's work/solution.
6. I have completed the problem and don't need help anymore. Thank you.
7. None of the above
alpine sable
#

1

lone heartBOT
#

@alpine sable Has your question been resolved?

alpine sable
#

!status

lone heartBOT
#
What step are you on?
1. I don't know where to begin.
2. I have begun but got stuck midway.
3. I got an answer but I was told that it's wrong.
4. I got an answer and would like my work checked.
5. I have a question about someone else's work/solution.
6. I have completed the problem and don't need help anymore. Thank you.
7. None of the above
alpine sable
#

4

alpine sable
#

<@&286206848099549185>

fading trench
lone heartBOT
#

@alpine sable Has your question been resolved?

lone heartBOT
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zinc willow
lone heartBOT
zinc willow
#

Could anyone tell where did I do my mistake as the answer is π/9,5π/9 and 7π/9

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<@&286206848099549185>

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why + and -

forest marsh
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Why did you write 5pi/3 ?

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Oh isee

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Ok

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Nvm

zinc willow
#

2pie - theta

forest marsh
#

Well you forgot the mod 2pi

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And when you divide by 3

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Became mod 2pi/3

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So pi/9 + 2pi/3

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Became 7pi/9

zinc willow
#

sry what does mod mean

forest marsh
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Modular

zinc willow
#

ooh

ocean sealBOT
forest marsh
#

This kind

zinc willow
#

is this like a rule for this specific math

forest marsh
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Cos(x) = cos(a)
=> x = +-a mod 2pi

zinc willow
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as i just stared trig

forest marsh
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Your circle is 2pi periodic

zinc willow
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ohh

forest marsh
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13pi/2 describe the same point than pi/2

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For example

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Also

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When you multiple or divide

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It affect the mod

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3x = 3 [9]
x = 1[3]

zinc willow
#

i really dont gett u as i just started like basic pure math trig

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could u use simpler terms 🤡

forest marsh
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Ok

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What didn't you get ?

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The mod thing ?

zinc willow
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yes

forest marsh
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Ok you see the unit circle ?

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If you do a whole turn on it

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Starting from one point

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You will end up at the same point

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Right?

zinc willow
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what is a unit circle

forest marsh
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The circle you use to know the values of cos and sin

zinc willow
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like the CAST chart

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?

forest marsh
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Idk what this is

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,w graph x² + y² = 1

forest marsh
#

Already seen it before ?

zinc willow
#

i was talking about this

forest marsh
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Well as long you see it as circle its good

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So

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You start from one point and you do a whole turn on the circle you will end up at the same point right ?

zinc willow
#

yes

forest marsh
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And what is a full turn in terms of rad angle

zinc willow
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umm idk

forest marsh
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What do you do if you turn on yourself to trickshot someone in a videogame ?

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What is it call

zinc willow
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😿 dont know

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dont play that much game

forest marsh
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Ok

nimble orchid
#

hello

forest marsh
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Its called a 360

zinc willow
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ohh

forest marsh
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But its in °

zinc willow
#

2pie

forest marsh
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Yessir

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So a full turn in trig speaking is 2pi

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So

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Now we know this imma introduce you to modular

zinc willow
#

okey

forest marsh
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This is JUST a notation to type +2kpi with k integers

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But we lazy

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So we use mod

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So

zinc willow
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ohh

forest marsh
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If you have lets say 5pi/2 = ... mod 2pi it is ?

zinc willow
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5/4

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-5/4

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?

forest marsh
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When you have something like this

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You want to know how much there is 2pi in 5pi/2

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So here

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5pi/2 = 4pi/2 + pi/2 = 2pi + pi/2

zinc willow
#

umm i dont get u like what are u supposed to when u inverse cosine something in radian

forest marsh
#

Wdym ?

zinc willow
#

in my math i did in the pic

forest marsh
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When you want to get the cos or sin out what you did is correct except that you forgot to put mod 2pi

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This mod 2pi is important cuz as we seen earlier it makes you have all the possible solutions

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So you have something like 3x = +-pi/3 mod 2pi

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Which is litterally

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3x = +-pi/3 + 2kpi

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And so

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If you divide by 3

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You have x = +-pi/3 + 2kpi/3

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And now you need to get all the values that are in [0,pi[ by changing values of k

zinc willow
#

so we use this mod2pie to get all the possible values of cosin

forest marsh
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All possible angles yeah

zinc willow
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what are the constant supposed to be

forest marsh
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The amount of whole turn you do

zinc willow
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and how do i know that amount

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w8 is it 3 times

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because 3 theta

forest marsh
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You don't need to know the amount, you replace k by integers value and if the result is in 0 pi you add it to solution set

forest marsh
zinc willow
#

u mean 1/3

forest marsh
#

?

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What 1/3

zinc willow
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the integer value

forest marsh
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1/3 isn't an integer

zinc willow
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w8 sry

zinc willow
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like this ?

forest marsh
#

And when you divide by 3 to get theta alone

zinc willow
#

yes

forest marsh
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You also divide the thing in the mod

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So it will be mod 2pi/3

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I don't like the use of arccos here tbh

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It make you forget one solution !

zinc willow
forest marsh
#

Cua you can't have the 5pi/9 else

zinc willow
forest marsh
#

No 2pi is the mod

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[] is notation

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Mod 2pi <=> [2pi]

zinc willow
#

could u again tell me how to get the other solution

forest marsh
#

Ok

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You have 3theta = +- pi/3 [2pi] right ?

zinc willow
#

like do i multiply the first solution with mod

zinc willow
forest marsh
#

You divide by 3

zinc willow
#

yes

forest marsh
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Giving you theta = +- pi/9 [2pi/3]

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Lets do the positive case first

#

So we have that for k = 0

#

Pi/9 is in 0,pi so its a sol

#

For k = 1

#

We have pi/9 + 2pi/3 = pi/9 + 6pi/9 = 7pi/9

#

Which is also in 0,pi

#

So its a sol

#

For k = 2 it won't be the case

#

So we stop here for the positive case

#

Lets do the negative

#

Theta = -pi/9 + 2kpi/3

#

k = 1 makes you have -pi/9 + 2pi/3 = -pi/9 + 6pi/9 = 5pi/9

#

Which is in 0,pi

#

So its a sol

#

For k = 2 it won't be the case

#

So we stop here

#

And we have all our three solutions

zinc willow
forest marsh
#

0 <= theta < pi

zinc willow
#

so it can be 1,2and 3

#

?

forest marsh
#

Theta is a real number

#

Not an integer

#

k is an integer

zinc willow
#

umm not getting it

forest marsh
#

How

zinc willow
#

is k 1,2and 3

forest marsh
#

That you choose in order to make theta in the set of values that theta can have

zinc willow
forest marsh
#

Yeah you can replace k by 2 and see that it will be greater than pi

#

And so its useless to continue further

#

Theta will always be taller than pi for k >= 2

zinc willow
#

yes got it

#

so we try until we reach the limit

forest marsh
#

Yeah

zinc willow
#

is it like a rule

forest marsh
#

You can also write 5pi/3 as you did

#

<@&268886789983436800>

forest marsh
#

Its just that for explain

#

Its better to have +- so that i can make things clearer between which case i do

#

Positive vs negative

zinc willow
forest marsh
#

The [2pi] are missing for the two first line else thats good

zinc willow
#

like this

forest marsh
#

Without k

#

Its either

zinc willow
#

why

forest marsh
#

[2pi] or + 2kpi, with k in Z

forest marsh
zinc willow
#

ohh

forest marsh
#

Choose the one that you rather do

#

They both the same

zinc willow
forest marsh
#

No +

#

Sry i miss it at the first time

zinc willow
#

ooh

forest marsh
#

Yep

#

Sure

zinc willow
#

i think i get it know

#

thx for explaining it my friend

forest marsh
#

You're welcome

zinc willow
#

. close

forest marsh
#

.close

lone heartBOT
#
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lone heartBOT
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waxen turtle
lone heartBOT
waxen turtle
#

Idk how to do it at all

high rapids
#

What do you know about probability?

waxen turtle
#

anddd

#

mean median and mode

#

and like quartiles

#

And number summaries

high rapids
#

Heard of conditional probability?

#

Maybe were used in those marble problems

dusty fox
#

lets hope this person heard of binomial distributions otherwise this will be a long one

honest nacelle
# waxen turtle

the probability of k successes in n trials is given by (n choose k) * p^k * (1-p)^(n-k), where p is the probability of success
think of being a homeowner as a success and the number selected as the number of trials

lone heartBOT
#

@waxen turtle Has your question been resolved?

waxen turtle
dusty fox
#

and you didnt have this in class?

gilded ore
#

Is this a basic statistics course?

lone heartBOT
#

@waxen turtle Has your question been resolved?

waxen turtle
waxen turtle
gilded ore
#

No I mean like dont they have a formula sheet?

lone heartBOT
#

@waxen turtle Has your question been resolved?

waxen turtle
gilded ore
#

Then idk what to tell you

#

But yea use binomial

modest fox
#

Is anybody free to help?

#

I need to know

#

If my constraint of 2x(5) + 2y(5) = 700 makes sense

#

10x + 10y = 700

#

y = 70 - x

#

A = xy

#

A = x(70 - x)

#

A = 70x - x^2

#

A'(x) = 70 - 2x

#

70 - 2x = 0

x = 35

modest fox
#

I get 1225

#

Which it says is wrong

#

<@&286206848099549185>

dusty fox
#

this aint yo fucking channel

#

get your own

lone heartBOT
alpine sable
#

I don't know who's channel this is but yes. Please get your own channel.

modest fox
#

Sorry

modest fox
alpine sable
modest fox
lone heartBOT
#

@waxen turtle Has your question been resolved?

waxen turtle
primal ore
#

what is a partial derivitive?

crude parrot
lone heartBOT
lavish cave
#

how did you get that?

#

you should be using the numbers 2, 1, 5 before you simplify

pseudo ice
wheat isle
lone heartBOT
#

@waxen turtle Has your question been resolved?

lavish cave
modest fox
# lavish cave that's not correct

To answer your question, I was not using the formula correctly

I was taking the 2x + 2y equation, and simply multiplying this by the cost of the respective sides

It should've acc just been (5x + 4y + y = 700) which equals (5x + 5y = 700)

I believe my answer was x = 70

#

And I forgot what y was

lavish cave
#

y is the height and x is the length of the field

gilded ore
#

So you have a set amount of trials which is 35 your probability of success (i,e home owners is .60) and your failure is 1-.60

gilded ore
#

Yea

#

Basically

#

N is 35 and K successes is 20 or whatever is defined by the problem

waxen turtle
#

im in bed but I'll try it in a bit Fr

north rover
#

3 hours?!

waxen turtle
#

im still in bed

clever folio
#

@alpine sable please don't delete mod pings

#

Please try to keep things mature here.

honest nacelle
#

like if you have 3 trials and one success you don't care whether your order of events is SFF, FSF, or FFS, so you multiply the probability by (3 choose 1)=3

#

the formula to compute (n choose k) is n!/(k!(n-k)!)

hazy echo
#

Can someone can help me with math hw quiz

sly bluff
hazy echo
sly bluff
hazy echo
sly bluff
#

I would suggest chatgpt

#

I barely started highschool 💀

modest robin
#

!nogpt

lone heartBOT
#

Please do not trust ChatGPT or similar AI tools for mathematical tasks, as they often generate output which "sounds correct" but has numerous factual or logical errors. Use of these AI tools to answer other people's help questions is strictly against server rules (see #rules).

modest robin
#

!occupied

lone heartBOT
#

Someone else is already using this help channel. If you need help with a question, please open your own help channel/thread (see #❓how-to-get-help for instructions).

hazy echo
#

can someone can help me with the math hw quiz

teal orbit
lone heartBOT
lone heartBOT
#

@waxen turtle Has your question been resolved?

modest robin
# waxen turtle

the answers to your question are parts of this sum as other helper have noted but for that to make sense you need to learn basic probability theory and from what I’m reading what is n choose k (the binomial coefficients).

#

$\sum_{k=0}^n \binom {n}{k} p^k(1-p)^{n-k}$

ocean sealBOT
#

pola_touche

modest robin
#

what you need imo in what I sent is part of unit 7 unit 8 and 9

gilded ore
#

The formula explains itself

#

n trials, k successes and the probability of success p

#

They defined in the problem that p = 0.6

#

n = 35

#

k is either 22 or the other numbers

#

You need to find

gilded ore
#

<@&268886789983436800> can somebody close this channel its been open for really long

tardy stag
#

it's not hurting anybody

gilded ore
#

And hadn’t attempted his problem or let us know of any progress

crude parrot
lone heartBOT
#

@waxen turtle Has your question been resolved?

#
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idle kettle
#

solved math ama

lone heartBOT
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static wagon
#

can someone tell me why for question 1, the answer is -2sqrt3/3 < x < 2sqrt3/3?

static wagon
#

i know it’s rationalised but why is x in between those two values

tropic plaza
#

Actually u made a slight mistake while putting f'(x) = 0

what u did-
3x²-4=0
x²= 4/3
x=2/√3

Actual solution-
3x²-4=0
x²= 4/3
x=±2/√3

Reason-
For eg. x²=4
We have two solutions x=2 and x=-2. U forgot to consider the negative solution

static wagon
#

ohhhh

tropic plaza
#

@static wagon ur pfp is haunting me

static wagon
tropic plaza
#

😭 👍 bye

static wagon
#

so am i meant to do two brackets?

#

one with the positive solution

tropic plaza
#

yes

static wagon
#

and one with the negative?

#

alr

tropic plaza
#

:)

#

3x²-4<0
x²<4/3
|x|<2/√3
So
-2/√3<x<2/√3

static wagon
#

yes got that

#

.close

lone heartBOT
#
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primal dagger
#

to solve the problem using method of undetermined coefficients i get that u have to like guess what the form on the left would be like (At+B) but how do you know like what ur guessing is correct ?

vale wigeon
#

you work out the roots of the characteristic equation as well as what characteristic values each term on the RHS would correspond to

primal dagger
#

the roots for this would be just 3,-1

#

and then i wrote it in the homogeneous solution

#

using the roots

#

and then i didnt know what to do with the right side for this like how to form a guess for the particular solution

sharp citrus
vale wigeon
#

right so the RHS corersponds to -1

#

so there is resonance

#

so you will need $(At^2 + Bt)e^{-t}$

ocean sealBOT
primal dagger
#

like everything else i understand but that

#

how did u know that it would be that that i need if my question makes sense

primal dagger
vale wigeon
#

ok right basically

#

terms of the form $P_k(t) e^{at} \cos(bt)$ or $P_k(t) e^{at} \sin(bt)$ correspond to the characteristic value $\lambda = a+bi$

ocean sealBOT
vale wigeon
#

where P_k is an arbitrary polynomial of degree k

#

the key is the multiplicity of λ as a root of the char eq

#

if λ is a root of multiplicity s, then your guess needs to be of the same form but contain a polynomial of degree k+s

#

(and both a sine and cosine term if b ≠ 0)

primal dagger
#

hm okok

mystic rivet
#

what is (a+b)whole cube

primal dagger
#

.close

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#
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dusk brook
#

Hi everyone!

I'm preparing for the entrance exam at the University of Bucharest, Faculty of Mathematics and Computer Science (Unibuc FMI). This is a problem from the 2023 admission exam, and I'm stuck on part (d).

Here’s the problem statement in English:

University of Bucharest
Faculty of Mathematics and Computer Science

Entrance Exam – July 2023

I. Algebra
Let the matrix
A = ( 4 2
-3 -1 )
be in M₂(R), and define the set
T = { xI₂ + yA | x, y ∈ Z },
where I₂ is the 2×2 identity matrix.

(a)
Prove the equality:
A² = 3A - 2I₂.
Determine the real number α such that:
(I₂ - A)² = α (I₂ - A).

(b)
Prove that the matrix
( 2 2
-3 -3 )
belongs to T, then check whether
( 4 4
-6 -3 )
is in T.

(c)
Show that for any natural number n ≥ 1, there exists a natural number xₙ such that:
Aⁿ = xₙ A + (1 - xₙ)I₂.

(d)
Verify whether the set { I₂ - A, -I₂ + A } forms a group under matrix multiplication.
Then, determine all two-element subsets of T that form groups under matrix multiplication.

vale wigeon
#

christ almighty! that text paste!

#

ok

#

so you want to check whether or not {I - A, I + A} forms a group under matrix multiplication

#

yes? is that what you're looking for?

dusk brook
#

Yes

vale wigeon
#

ok do you know what a group is

dusk brook
#

yes

vale wigeon
#

ok can you tell me what properties a group must satisfy

dusk brook
#

a moment

#

To be associative, to have a neutral element, and to have an invertible element.

vale wigeon
#

ok

#

when the operation is matrix multiplication, what should the neutral element be?

dusk brook
#

I

#

identity matrix

#

right?

#

I have (more or less) proven that it is a group, but I have a problem with the next part:
Then, determine all two-element subsets of T that form groups under matrix multiplication.

vale wigeon
#

I have (more or less) proven that it is a group,
you have?

#

how can you have proven that {I-A, I+A} is a group when the identity matrix I doesn't belong to this set???

dusk brook
#

Whait, I worked on this problem some time ago.

vale wigeon
#

aaaaaaa

dusk brook
#

English is not my first language; I use a translator.

vale wigeon
#

whatever translation software you're using, it completely destroys all the math notation you feed into it

#

making it absolutely unreadable

dusk brook
#

I defined
x= I2 − A
and
y = −I2 + A
then I computed
x⋅x, y⋅y, x⋅y, y⋅x, and
From this, I found that the neutral element is
𝑦.

vale wigeon
#

so you found that y^2 = y and xy = yx = x...?

dusk brook
#

yes

vale wigeon
#

hm

#

ok, looks like it is a group, despite neither matrix being the identity...

#

wait, what did you get for x^2?

dusk brook
#

I have proven that it is a closed set under multiplication, that it is associative, and that it has a neutral element, but proving the existence of an invertible element... that's where I'm stuck.

vale wigeon
#

i don't see your calculation for x*x

dusk brook
#

yea...

vale wigeon
#

so you got xx = y

dusk brook
#

yea

vale wigeon
#

and y is the neutral

dusk brook
#

yes

vale wigeon
#

therefore, within this group, x is its own inverse

dusk brook
#

ooooo

#

I see

#

Now, I have a problem with the next part:
Then, determine all two-element subsets of T that form groups under matrix multiplication.

vale wigeon
#

ok that one looks quite difficult without some brute force sorry

dusk brook
#

I think we need to use this from the previous subpoint
A^n = x_n * A + (1 - x_n) * I_2

#

or

#

where α = -1

lone heartBOT
#

@dusk brook Has your question been resolved?

dusk brook
#

<@&286206848099549185>

University of Bucharest
Faculty of Mathematics and Computer Science
Admission Exam – July 2023

I. Algebra.
Let the matrix
( 4 2 )
A = ( -3 -1 ) ∈ M_2(R)
and the set
T = { x · I_2 + y · A | x, y ∈ Z },
where I_2 is the identity matrix of order 2.

(a) Prove the equality:
A^2 = 3 · A - 2 · I_2.
Find the real number alpha ∈ R such that
(I_2 - A)^2 = alpha · (I_2 - A).

(b) Prove that
( 2 2 )
( -3 -3 )
belongs to T, then verify whether
( 4 4 )
( -6 -3 )
belongs to T.

(c) Show that for any natural number n, n ≥ 1, there exists a natural number x_n such that
A^n = x_n · A + (1 - x_n) · I_2.

(d) Verify that the set { I_2 - A, -I_2 + A } forms a group under matrix multiplication. Then, determine all subsets of T with two elements that are groups under matrix multiplication.

#

I need help with d)

lone heartBOT
#

@dusk brook Has your question been resolved?

kindred anchor
#

<@&268886789983436800>

vale wigeon
#

<@&268886789983436800> advertising

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#
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quasi oak
#

is this correct?

lone heartBOT
vale wigeon
#

seems so

quasi oak
#

thanks

lone heartBOT
#

@quasi oak Has your question been resolved?

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lilac stag
lone heartBOT
lilac stag
#

how do i tell based of this data

#

how many people watched a serie in the past month for

#

less than 2 times

#

2-10 times

#

and more than 10 times

#

I dont understand at all

twin nimbus
#

So the box and whisker plot will tell you the quartiles

lilac stag
#

Yes

twin nimbus
#

So 25% watch less than 2 times

lilac stag
twin nimbus
#

Because the whisker extends from 0 to 2

#

and the whisker represents 25% of the population

lilac stag
#

Wait

#

This

#

Part, is it that part your talking about

twin nimbus
#

yes

lilac stag
#

How does it show 25

#

procent

twin nimbus
#

that's just what the whisker represents

#
---|     |     |-----
25%   25%  25%    25%
lilac stag
#

hmmm

#

Wait

#

Let me draw

twin nimbus
#

bbiab

lilac stag
#

This is how I have understood it

#

Less than 2 times then we are talking about 0-2 right? but theres nothing there not a box nothing. Thats where my brain goes blank @twin nimbus

odd lion
#

Isn't the green box represents how many peoples actually watched the film between 2 to 10 times which is 40% total!!

lilac stag
#

With ur method I can see that you split it up too 4 parts where all is 25% even though they arent as big as each other

lilac stag
#

Thats what it says on the answer sheet

#

But I dont know how to interpret it,

#

Cause the parts are not as big as each other

odd lion
#

@lilac stag oh I see my bad

lilac stag
#

All good

twin nimbus
#

hi I'm back

#

so the green box is a total of 50% of people

#

you have the 25th to 75th percentile in the box

#

0 to 25 in the whisker under the box

#

75 to 100 in the whisker above it

#

@lilac stag

lilac stag
#

i think i get

#

it

twin nimbus
#

nice!

lilac stag
#

yes

#

since it goes from 25% to 75%

#

it must be 50%

twin nimbus
#

yup

lilac stag
#

thats the part I get now

#

And the one from 0-2 that looks obv like 25%

#

the only thing left is more than 10 and that looks so weird but the only reasoning we have there is

#

100-75=25?

twin nimbus
#

so what might be throwing you off

#

is that it's not balanced.

lilac stag
#

yes

twin nimbus
#

But the data isn't balanced, instead think about it this way. Let's say we have 100 people

#

let's say 15 people watched 0 movies, and 10 watched 1 movie.

#

13 watched 2 movies, 12 watched 3 movies,

lilac stag
#

mhm

#

but im just scared, now that i learned this that an even more unbalanced box or whatever its called pops up

twin nimbus
#

10 watched 4 movies, 4 watched 5, 5 watched 6, 2 watched 7, 2 watched 8, and 2 watched 9

#

when the box is large, that means the values are less clustered.

#

the same amount of people are stretched thinner.

lilac stag
#

ok ty

vale crag
#

<@&268886789983436800> huge spam

lone heartBOT
#

@lilac stag Has your question been resolved?

lone heartBOT
#
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#
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limber willow
#

Hi

lone heartBOT
limber willow
#

could someone explain to me how the y-intercept was calculated? this is a graph representing f(x) = 3x-5/x-5. in part c, i had to show that f(x) is an inverse function. however, in this task, i had to graph this function and draw all asymptotes/intercepts.

from my calculations, the y-intercept is (0,1) but it's (0,5/3)

tacit arch
#

is that your function

ocean sealBOT
#

riemann

limber willow
tacit arch
#

,w plot (3x - 5)/(x-5)

#

did you get the function wrong?

limber willow
tacit arch
#

can't tell unless you show the function

limber willow
#

point d, so i calculated that it is an inverse function. i set y to 0 to calculate the x-intercept, which is (5/3, 0) and it's correct. after that, i set x to 0 to calculate the y-intercept, which gave me (0,1), which is wrong

lone heartBOT
#

@limber willow Has your question been resolved?

limber willow
#

<@&286206848099549185>

#

okay i got it now i wrote the number down 😭 thank you

#

.close

lone heartBOT
#
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winter umbra
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Whats 0!

lone heartBOT
crude parrot
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1

twin nimbus
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1

winter umbra
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Would it not be 0 becae 0×0 is 0

crude parrot
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definition of factorial

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how many ways can you arrange x objects

twin nimbus
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Instead, think of it as the number of ways you can reorder 0 objects

crude parrot
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you can only arrange 0 objects in one way

vale wigeon
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the definition of factorial is tricky to apply to zero objects

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i like to think of it as "the product of nothing is 1"

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just as the sum of nothing is 0

twin nimbus
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Oooh, that's good

winter umbra
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👍

worthy void
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hallo

lone heartBOT
#

@winter umbra Has your question been resolved?

lone heartBOT
#
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Remember:
Ask your math question in a clear, concise manner.
Show your work, and if possible, explain where you are stuck.
After 15 minutes, feel free to ping <@&286206848099549185>.
• Type the command .close to free the channel when you're done.
• Be polite and have a nice day!

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blazing widget
lone heartBOT
blazing widget
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thx

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not sure how to solve this

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Modeling with linear equations and inequalities

lone heartBOT
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@blazing widget Has your question been resolved?

alpine sable
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I can help

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149-95t
170-110t

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2 expressions

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We can then plug in

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Values

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For example 1, chimiake is faster, 2 chimiake is faster

tacit arch
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<@&268886789983436800>

alpine sable
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What is this

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What was that

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Was that a phiser

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Or smth

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I took a photo

sly mantle
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they ded

alpine sable
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Ok

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Yo

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Is the work above correct

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Nvm

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Oh I did it wrong

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149-95t 170-110t

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We can say

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That oringinal Ly

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149-95t is greater than 170-110t

blazing widget
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this is the answer I got

alpine sable
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Uh

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Yes

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After we can simplify

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1.4=t

blazing widget
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how did you simplify it

alpine sable
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Divide 21 by 15

blazing widget
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yes

alpine sable
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It’s a fraction

blazing widget
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is that all the steps

alpine sable
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We can divide

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Yes

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U want me to explain it

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To u

blazing widget
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1.4 hours

alpine sable
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How I got 1.4

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Uh yea

blazing widget
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t<1.4?

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or greater then

blazing widget
alpine sable
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Uh

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The whole problem

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?

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T is not equal

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To 1.4

blazing widget
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yes

alpine sable
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Ok

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So first

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We can get the expressions

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Post this here rq

blazing widget
alpine sable
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Ok

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We get the expression 170-110t is less than 149-95t

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So we can fight at what value can t be less than

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170-110t can eventually be greater

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But we need to find out what t can the greatest of t can be

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My grammar

blazing widget
alpine sable
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So after doing that

blazing widget
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how can t eventually be greater

alpine sable
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Like 1.5

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Plug it in

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170-110(1.5’

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149-95(1.5’

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As u can see

blazing widget
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nah I might need to skip this lesson

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this is mad confusing

alpine sable
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Wait lemme write it out

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It easier

alpine sable
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Later u will need to do complex distance

blazing widget
alpine sable
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Alr

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Finished

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Tell me if u got questions

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@blazing widget we good?

blazing widget
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thank you

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what in the beginning equation gave you greater than sign

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like what word

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or phrasing

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@alpine sable

alpine sable
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?

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Oh

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Hmmm

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Well

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It’s to tell us like

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What the greatest value of t would be if chimiake was closer than valente

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Then after

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Yea

blazing widget
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what do you mean

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im saying like what word here tells you this is an inequality

alpine sable
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Oh

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It’s because

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We wanna find

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When

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When valente is closer than chimiake to the university

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And then we can say

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When valente is closer it means the distance is less

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And chimiake is tester

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Greater

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So we say

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I’m getting confused now lol

blazing widget
alpine sable
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Bro

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Ah hell nah

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U can get banned for that

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It’s very hard to explain to a 5th grader

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😭

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Where u even find this

blazing widget
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Im trolling

blazing widget
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You don’t truly know math until you can explain it to a 5th grader

alpine sable
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What grade are u even in

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?

blazing widget