#help-43

1 messages · Page 42 of 1

quartz yoke
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The only hard one to get is <PQA

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you can notice that ||CQ bisects <PCM (you probably already know this) and MQ bisects <PMC (given in the statement). So what do these 2 things imply?||

compact pewterBOT
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@icy topaz Has your question been resolved?

icy topaz
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That Q is the incentre of the triangle PMC

quartz yoke
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this should allow you to angle chase and find <PQC

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then you can do this

icy topaz
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Got it.

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Thanks.

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.close

compact pewterBOT
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compact pewterBOT
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forest token
compact pewterBOT
native shard
forest token
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adding x^3 and subtracting x^3 to that first integral

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and then i thought x^3-sin^3x ill write as (x-sinx)(x^2+sin^2x+xsinx)

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but i didnt know what to do from there

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@native shard

forest token
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yea thats what i meant

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how do i proceed

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or start

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ykw just leave it

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.close

compact pewterBOT
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compact pewterBOT
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strange pendant
compact pewterBOT
twin idol
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Do you know the formula for summing the natural numbers from 1 to n?

strange pendant
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n(n+1)/2

twin idol
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Ye

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Q 3 will need you to use it

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Also use the fact that summation is linear

strange pendant
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can you elaborate

twin idol
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$\sum_{i = 1}^n ki = k\sum_{i = 1}^n i$

boreal girderBOT
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VulcanOne

strange pendant
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what about it

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how do I do i) for example

twin idol
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You will need to use this fact to deconstruct the summation

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And make it easier to use the formula

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Also

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$\sum_{k=1}^n \left(k + c\right) = \left(\sum_{k=1}^n k\right) + \left(c\sum_{k=1}^n 1\right)$

boreal girderBOT
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VulcanOne

twin idol
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@strange pendant

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Stop playing osu and focus here

strange pendant
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dude can you help me

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step by step please

twin idol
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You will need to focus on the problem so I can help

strange pendant
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I am focused, 100%

twin idol
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On osu that is

strange pendant
twin idol
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I gave you the 2 most important facts for Q 3

twin idol
twin idol
strange pendant
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well

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how do I join the pieces together then?

twin idol
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Well

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Use fact 2

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Then use fact 1

strange pendant
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how ?

twin idol
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I want you to reach the answer by yourself Renato

strange pendant
twin idol
strange pendant
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@twin idol

twin idol
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Now take n as a common factor

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Can you do ii in the same way?

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@strange pendant

strange pendant
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how?

twin idol
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ii has a bit of a trick up its sleeve

strange pendant
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dude HELP

twin idol
strange pendant
twin idol
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You did well

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Now are you able to do 2 in the same way?

strange pendant
twin idol
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Yeah

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Can you do it in the same way?

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I'll need to give you another fact

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Because of the trick

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$\sum_{k=c}^n k = \left(\sum_{k=1}^n k \right) - \left(\sum_{k=1}^c k\right)$

boreal girderBOT
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VulcanOne

twin idol
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@strange pendant yeah please exit osu for now

strange pendant
twin idol
twin idol
strange pendant
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now what?

strange pendant
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are you in osu dude?

twin idol
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Nop

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I'm not on osu

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4 hours and I'll go to my work week

twin idol
twin idol
strange pendant
twin idol
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Now apply formulas

strange pendant
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now what dude

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I need a fact number 4

twin idol
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Nah all the facts are given

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No need for fact 4

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Fact 4 is gonna be for Q4

strange pendant
strange pendant
twin idol
twin idol
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Make sure to evaluate the sum from 1 to 6 of 5

strange pendant
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how

twin idol
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Well

strange pendant
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please elaborate

twin idol
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The same formula you used for $\sum_{k=1}^n 5$

boreal girderBOT
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VulcanOne

twin idol
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But instead of n it will be 6

strange pendant
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?

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what about the 5

twin idol
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$\sum_{k=1}^6 5$

boreal girderBOT
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VulcanOne

twin idol
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Evaluate it

strange pendant
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5*6

twin idol
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Yeah

strange pendant
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lmfao

twin idol
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Lmfao

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Now simplify

strange pendant
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@twin idol @twin idol @twin idol @twin idol @twin idol

twin idol
strange pendant
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NOW WHAT

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@twin idol

twin idol
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Now we can get into Q4

strange ermine
strange pendant
compact pewterBOT
strange pendant
strange ermine
strange ermine
strange pendant
cerulean bramble
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He's gonna be at work

twin idol
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for a week straight

strange pendant
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I didnt know

twin idol
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Alright now let's move on to Q4

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$\sum_{k=0}^{n-1} p^k = \frac{1-p^n}{1-p}$

boreal girderBOT
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VulcanOne

twin idol
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Fact 4

strange pendant
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I dont think I can take this as true

twin idol
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Why not?

strange pendant
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I dont see how is this true

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I dont think I follow

twin idol
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This is the sum of a geometric series from k = 0 to n-1

strange pendant
twin idol
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Check the indices

strange pendant
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well

twin idol
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I gave you the sum with different indices. It's a correct formula.

twin idol
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For the used indices

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Anyways

twin idol
strange pendant
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how did you came up with this?

twin idol
twin idol
strange pendant
twin idol
strange pendant
twin idol
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Buddy I'll have to leave now. I gotta do some stuff before going to work

strange pendant
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$\sum_{k=0}^{n-1} p^k = \frac{1-p^n}{1-p}$

boreal girderBOT
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Renato

twin idol
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Let j = k+1

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$\sum_{j=1}^n p^j = \frac{1-p^n}{1-p}$

boreal girderBOT
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VulcanOne

twin idol
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Same thing

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Anyways gotta leave now

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Good luck. You can do this on your own I know that

strange pendant
compact pewterBOT
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@strange pendant Has your question been resolved?

#
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frank root
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Did I set this up right?

compact pewterBOT
vivid breach
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also, go show your answers for (a) through (d) before we consider (e)

frank root
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A. 15,957 B.797.85 C.”It measures the rate of change of people” D.9092.15

vivid breach
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(c) is too vague, theres multiple ways to measure that rate of change

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you need to be specific that its the average rate of change from 1980 to 2000

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(d) btw is exactly the same as (b)

frank root
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Alright so we’re back on question e

vivid breach
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you know why (d) = (b), right?

frank root
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The average rate of change divided by 20 right?

vivid breach
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the average rate of change already includes a /20, as you did in (b), so no

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you dont divide the average rate of change by 20 a second time

frank root
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Can u help me on e now?

vivid breach
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do you know what average rate of change is

frank root
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797.85

vivid breach
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a number isnt going to convince me you know why its supposed to be like that

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where did you even get 9092.15 from

frank root
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181843/20

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is where i got 9092.15 from

vivid breach
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oh alr, thats wrong but I see you wont be doing that anymore

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now for this

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unless youre a fan of writing down numbers with decimals on paper all the time, we gotta get the calculator to do this for us

frank root
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i got desmos pulled up

vivid breach
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now the best-case scenario is telling the calculator a and b and it tells us back the average rate of change

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to do this, we have to make something that can calculate this

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sort of plan the calculation out

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lets say youre figuring out the average rate of change on [5, 10]

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what would you calculate to get this answer?

frank root
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797.85-2000/10-5?

vivid breach
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also dont forget ()s

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for average rate of change on [5, 10], you need (something) / (10 - 5)

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797.85 - 2000 is not the correct idea

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we're nto considering average rate of change of average rates of change

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first,

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do you understand this part of the problem

frank root
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That's the formula I should be using

vivid breach
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surely theres more to P(t) than "oooh its a formula"

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maybe that it means something about the population?

frank root
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p(t)=population

vivid breach
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P(5) represents the population in what year?

frank root
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1985?

vivid breach
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yea

vivid breach
frank root
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(1985-1.04) / (10 - 5)?

vivid breach
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???

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why 1985?

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are you just coming up with random things to put in the numerator?

frank root
vivid breach
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Im asking you that because, no, you dont just put 1985 - 1.04 for the numerator

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lets try something else

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earlier you said P(5) means the population in 1985

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so we have a way to go between 5 and the year 1985

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based on that, [5, 10] represents what 5-year span?

frank root
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1980

vivid breach
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1980 is not a "5-year span"

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1980 is just a single year

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lets restart

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10, what year does this represent?

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(you already know 5 represents the year 1985)

frank root
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1990

vivid breach
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good

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[5, 10] is a closed interval from 5 to 10

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what does that mean?

frank root
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1985-1990

vivid breach
frank root
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I went backwards instead of forward

vivid breach
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??????????????

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thats a bold move

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anyways [5, 10] represents 1985 to 1990

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so since P(t) represents the population in 1980 + t,

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P(5) represents the 1985 population
P(10) represents the 1990 population

frank root
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(1990-1985) / (10 - 5)?

vivid breach
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those are just the years

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thats 1

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thats saying 1 year happens every year, on average

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think about what youre doing

frank root
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mb

vivid breach
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let me continue

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so P(5) tells us the population at the beginning of [5, 10]

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and P(10) tells us the population at the end of [5, 10]

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we know the years that these represent, but we dont need to use that information for now

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I was just giving context for what this (otherwise vague) thing means

vivid breach
frank root
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P(5) is the population at the beginning of the interval [5,10]

vivid breach
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right

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we can calculate P(5) to be 185444
and P(10) to be 189117

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so whats the average rate of change for the population from 1985 to 1990?

frank root
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where did u get these numbers from 185444 189117

vivid breach
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I want you to actually know what this image means

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read this closely, what does this mean?

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theres not like a hidden message or anything, I just want you to know what P(t) even is supposed to be about

frank root
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you just multiplied 181843(1.04) and got 189117

vivid breach
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kaleb you do see the big formula in the middle of the picture right

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P(10)

frank root
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so you just replaced t with 10 and did the same with 5?

vivid breach
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yes, thats how you use a function

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moving on,
185444 is the population in 1985
189117 is the population in 1990
so whats the average rate of change in population from 1985 to 1990?

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going to remind you btw that you didnt have a problem with this problem when it was phrased like (b), so this time you have no excuse

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look back on the calculation you did for (b) if youre stuck on finding this rate of change

frank root
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734.6

vivid breach
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there you go

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now lets consider another problem with the way we're doing things

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remember that we were trying to plan out a calculation, right?

frank root
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yes

vivid breach
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when I ask, all youre giving are the ending results

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you didnt show what you did

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we cant plan just on the final result

frank root
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how do i sc again

vivid breach
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Win + Shift + S

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theres an option in the windows settings to remap this to the PrntScreen button, if you want

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not sure if itll do the same thing though
last time I checked, PrntScrn copies your entire screen to your clipboard

frank root
vivid breach
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ideally you dont want to reveal your entire screen

frank root
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mb

vivid breach
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select an option at the top of the Win + Shift + S menu to change which kind of selecting you can

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default option is whole screen, but you can also chosoe to screenshot a window or screenshot a rectangle of your choice

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Im screenshotting rectangles with Win + Shift + S to get my pictures

frank root
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ok thanks

vivid breach
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we change the denominator to 10 - 5 instead

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that way, its closer to the t we used

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10 - 5 and 1990 - 1985 both calculate a 5-year difference

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since the units are in years

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now for the final change

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189117 and 185444 werent just any numbers

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we had to calculate them, from a formula

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what function gave us those two numbers?

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you dont have to write out the whole formula or anything, you can just mention the function

frank root
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P(10)=181843(1.04)^t/10

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mb

vivid breach
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dw

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youre being precise

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youre forgetting ()s though, ^(t/10) instead

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and that t should be a 10 as well

frank root
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wouldnt that just be 1 for 10?

vivid breach
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yep

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dont simplify it though

frank root
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alr

vivid breach
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we're going to leave that up to the calculator

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really, this is our formula

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keep in mind what we based this all on: (b)

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(b) had you do the same kind of calculation for the average rate of change

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now we see the same formula again, but for P

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(P(b) - P(a)) / (b - a) finds the average rate of change of the function P from a to b

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on [a, b]

vivid breach
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from here, Ill show you two ways you can get the calculator to calculate this

frank root
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ok

vivid breach
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first, by default desmos doesnt know what P is

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define the function P in a separate line

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desmos then knows that its a function, so P(5) and P(10) can be calculated

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for desmos in particular, use x for the input variable

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using another variable (like t) might mess things up if you use t for something else

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to further shorten how much we need to do, replace 5 and 10 with a and b

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that way instead of replacing both 10s with 9s, you can just replace the =10 with =9

frank root
vivid breach
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yep

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theres a closely-related second way to this

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take a look at the guess you started with

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I dont understand how you cooked any of this to the way it is

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but does look like you want to reduce it all into as few lines as possible

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all in one big formula

frank root
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Trial and Tribulations

vivid breach
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Trials and Tribulations

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consider instead if we had something like this

frank root
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little too advanced for me

vivid breach
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compared to the previous one, theres a lot more going on here, but its the same calculation

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this is a function that takes in two inputs

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it is written f(x, y)

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f(5, 10) will have the input x=5 and y=10

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yes?

frank root
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yes

vivid breach
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second

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this is just P(y) - P(x), isnt it

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you dont seem to recognize it given your immediate reaction

frank root
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yeah but i probably wouldnt come up with this on my own

vivid breach
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my brother in christ, you copy-paste P into there

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you can come up with copy-pasting

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thats all I did, nothing more

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youre seeing what Im seeing right? I didnt do any further steps than just writing down P(t) into there

frank root
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yes i can see that

vivid breach
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wdym "come up"?

frank root
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like for me I see all the steps i did to come up with answer to actually understand it

vivid breach
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well we didnt reach the final step yet

vivid breach
frank root
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wym

vivid breach
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sure

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final thing, instead of a and b we use x and y

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no big reason other than for desmos to like it better

frank root
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Oh alright

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I put in the other numbers thats it right?

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for the problem

vivid breach
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yep

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we made the function so that you can do that

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f(5, 10) for [5, 10]

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you can also see the function so you can be sure that its calculating the right thing

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its doing (P(y) - P(x)) / (y - x) for the x and y you put in

frank root
vivid breach
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(P(a) - P(b)) / (a - b) also works

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you can multiply by -1 / -1 to swap between this and the other one (P(b) - (a)) / (b - a)

frank root
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But what I did is correct right?

vivid breach
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yea

frank root
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Alright thank you so much for your help idk how u put up with me I was trying but some of this just didn't make sense to me

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and im just using my calculations i used for part E on part F right?

vivid breach
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(f) has you do something different

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consider this

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(f) wants you to consider how the numbers change as you go from [5, 10] down to [5, 6]

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then use that to guess what the "instant" rate of change at 1985 is

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now f(5, 5) wont work, since thats a rate of change with / (5 - 5) which divides by 0

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so they want you to roughly estimate it from these

frank root
#

Its getting closer to 727

vivid breach
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you can also just do f(5, number really close to 5)

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it gets close to 727.596

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Im not too sure what they mean by the second question

frank root
vivid breach
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yep

vivid breach
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seems too easy

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but it should be correct

frank root
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Alright thank you

vivid breach
#

np

frank root
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Don't go to far ill be back tomorrow your one of the best tutors I've ever had

compact pewterBOT
#

@frank root Has your question been resolved?

#
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Ask your math question in a clear, concise manner.
Show your work, and if possible, explain where you are stuck.
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hushed tapir
#

I need help with part 2 of question 1.5. This is real analysis 1

hushed tapir
#

<@&286206848099549185>

old mica
hushed tapir
#

Yes

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I’ll send it right now

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I think it’s wrong though

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Would you like to see my professor’s hints?

old mica
upper bane
#

you are claiming that sup(X) = 1/3, right? why not find the difference between 1/3 and f(x) in terms of x?

old mica
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we'd like to show that if s > z, then z isn't an upper bound of X - that's not the same as proving that no element of X is an upper bound for X

hushed tapir
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We haven’t learned functions yet @upper bane

upper bane
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replace f(x) with that expression

hushed tapir
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I’m just confused where to start

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And where to go

old mica
# hushed tapir Huh?

you assumed that z has the form (x^2 - 1)/(3x^2 - 1), when this doesn't have to be the case MiniheraBow

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as for what to do, Hanako's suggestion is useful

upper bane
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the idea is, you want to prove that sup(X) = 1/3, so you have to prove that there is no z < 1/3 that is an upper bound

hushed tapir
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Here’s what my professor wants me to do

upper bane
boreal girderBOT
#

Hanako

upper bane
#

from there, the difference between 1/3 - z is exactly the difference between 1/3 and the expression found earlier

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and we want this difference to be smaller than epsilon

old mica
# old mica as for what to do, Hanako's suggestion is useful

here's a more explicit plan of action:

first, prove that the sequence (n^2 - 1)/(3n^2 - 1) converges to 1/3. spoilers for the rest: ||then if z < 1/3, the distance from 1/3 to z, given by the difference |1/3 - z|, is equal to some positive number epsilon. but since that sequence converges to 1/3, the difference between (n^2 - 1)/(3n^2 - 1) and 1/3 goes to 0 as n goes to infinity, so for a sufficiently large value of N, you can pick an element of X that's larger than z (distance to 1/3 is less than epsilon), hence z isn't an upper bound.||

hushed tapir
#

I can’t use sequences

old mica
#

then what can you use?

hushed tapir
#

It’s like very limiting with what I can use

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The definition of LUB

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And ordered sets

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The hints doc I sent pics of lays out kinda what I should do

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Also, Archimedean property could be useful

old mica
#

I must apologize for misleading you then MiniheraBow

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I don't think I can figure out a way to do this problem with what you have sadcatthumbsup

hushed tapir
#

Then what should I do

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I’ve been stuck on this one

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I can show a problem where I proved GLB, which might help

#

<@&286206848099549185>

quiet minnow
hushed tapir
#

I need help with this analysis problem, and other people can’t figure out how to do it with my current level of knowledge

compact pewterBOT
#

@hushed tapir Has your question been resolved?

hushed tapir
#

No

#

<@&286206848099549185>

twin anchor
#

can you repost the question and your progress so far

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im not sure how far youve gotten

hushed tapir
#

I have basically no progress

upper bane
#

i have an attack plan, but i don't know if i'm correct

#

sorry

hushed tapir
#

It deals with smth like this

twin anchor
#

it seems like you have a lot written

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thats good

hushed tapir
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I only proved that it’s a upper bound, not that it’s a LUB

twin anchor
#

okay, cool

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there's 2 ways to show that an upper bound s is a LUB

way 1: show that all other upper bounds are >= s

way 2: show that any number < s is not an upper bound

I think way 2 is easier here

hushed tapir
#

That’s what the professor said

twin anchor
#

let's try that then

hushed tapir
#

Did you read the hints?

twin anchor
#

let's take some number less than s. call it s - ε for some ε > 0

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no, do you want me to? i have a fairly certain idea of how to go about this but if theres a specific way you want this done we can look at that

hushed tapir
#

Can you? It’ll give kinda an idea of how he wants it. I only just started analysis so we have learned: ordered sets, LUB GLB, BFA, and archemdian property

twin anchor
#

that seems like enough

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where are the hints

#

is that the red

hushed tapir
#

Yeah, it’s typed

twin anchor
#

everything they said seems pretty reasonable and normal

#

i dont think theres a special way you have to do this

hushed tapir
#

So what should I start doing

hushed tapir
#

I have that already, I called it z

twin anchor
#

we want to show that for some n in N, (n^2 - 1)/(3n^2 - 1) > 1/3 - ε

#

i think it might be easier to work with 1/3 - ε instead of z

#

because then you isolate a positive part and the limiting part

hushed tapir
#

Why would that prove this

twin anchor
#

are you asking why we want to show that for some n, (n^2 - 1)/(3n^2 - 1) > 1/3 - ε ?

#

or why i decomposed it

#

into 1/3 and ε

hushed tapir
#

So you’re saying trying to find an x s.t. It’s inbetween the LUB and some variable ε

twin anchor
#

no, let's just use your z variable

upper bane
#

(sorry to bother, but when you're done, snowflake, could you pls look in bots and see if my version works? thank you, and sorry for imposing. it's ok if you can't though!)

twin anchor
#

i want to show that for any z < 1/3,

(n^2 - 1)/(3n^2 - 1) > z

for some n. I just want to show that z isn't an upper bound, and this is the definition of that

hushed tapir
#

Yes

#

I understand

twin anchor
#

okay great. it's just equivalent that if z < 1/3, then I can write z as 1/3 - ε for some ε > 0, and then the inequality just becomes finding n such that

(n^2 - 1)/(3n^2 - 1) > 1/3 - ε

which is equivalent to finding n such that

ε > 1/3 - (n^2 - 1)/(3n^2 - 1)

and it's generally easier to aim for something to become arbitrarily small/close to 0 than to work around an annoying variable like z that has implicit stuff floating around it

#

that's just the motivation I had for decomposing it, it makes things a little more straightforward this way

#

for all ε > 0, we just need to find some n such that 1/3 - (n^2 - 1)/(3n^2 - 1) < ε

#

do you still follow

hushed tapir
#

Yes

twin anchor
#

great

hushed tapir
#

Let me write down you’re thinking real quick

#

Why are we allowed to make this equality

#

We don’t know if such n exists yet

twin anchor
#

this is the goal, we don't know this works yet

#

the goal is to obtain an n that makes this true

#

if it does, then we've found an n that disproves 1/3 - ε being an upper bound

#

if we can do this for arbitrary ε, then 1/3 must be the LUB

#

a common method (the common method) in analysis is to "work backwards" from inequalities that you want to be true, to solve for appropriate conditions that make them true

#

since for each ε, we only need to find a single n that satisfies the inequality, we have a good amount of flexibility to solve for valid n

#

does that makes sense

hushed tapir
#

Yeah, so we use the inequality we want to be true to solve for something? That seems circular

twin anchor
#

no

#

we are not using the inequality at all yet

#

we are going to use basic facts to prove the inequality for some n first

#

then, we can use the inequality to prove our claim that 1/3 is the LUB

#

the trick here though is that often times, operations on inequalities and equations are "invertible"

#

we can obtain equivalent inequalities by adding the same thing to both sides for instance, or multiplying by a nonzero number

#

the idea is if we can do some "allowable" manipulations to this inequality, constantly "thinking backwards" about what these manipulations imply, then we can eventually find some n that will directly imply the original inequality

#

you did this all the time in grade school

when i want to solve 3x > 18 for x, I first look at 3x > 18, and then divide by 3 to get x > 6, right?

maybe that seems circular. I started with 3x > 18 to find x values that satisfy 3x > 18, how does that work?

well, because dividing by 3 is an invertible operation on inequalities, I knew I could always just work backwards from wherever I end up to get the inequality I wanted

hushed tapir
#

Alright

#

So how does it apply here

twin anchor
#

we havent even gotten to the solving step yet

hushed tapir
#

Yeah

twin anchor
#

this is the important logical understanding

#

okay

hushed tapir
#

It’s the goal?

twin anchor
#

yes

#

but we're gonna try manipulating it directly first

#

in ways that we can easily reverse

#

or at least reason about

#

so that we can find valid n that we can apply the steps in reverse for to get the desired goal

#

so let's start manipulating it

hushed tapir
#

Yes!

twin anchor
#

ideally, we get the n by itself

#

a polynomial / a polynomial is pretty annoying

#

do you have any ideas on how to make it simpler

hushed tapir
#

We should create a simpler rational fraction

twin anchor
#

yup

hushed tapir
#

n^2-1/3n^2

#

It’s gonna be smaller

twin anchor
#

that isn't something we can legally do though

#

we need valid operations

#

you could potentially make an argument to do that, what would your argument be

hushed tapir
#

Idk

#

That’s what the hints said to do

twin anchor
#

right, youre close already

twin anchor
hushed tapir
#

n^2-1/3n^2-1 > n^2-1/3n^2

twin anchor
#

if that was true, that wouldnt be helpful for us

#

if I only know that c < a, I can't use c in any way to prove that a < b

#

if c > a, then i could just prove c < b to show a < b

twin anchor
hushed tapir
#

Why?

twin anchor
#

oh wait your denominator includes -1

#

do you know latex?

hushed tapir
#

I didn’t include parenthesis, want me to rewrite

#

Yeah but my computer is far and my roommate is sleeping

twin anchor
#

parentheses would be rlly helpful yeah

#

$\frac{n^2 - 1}{3n^2-1} > \frac{n^2-1}{3n^2}$

boreal girderBOT
#

snowflake

twin anchor
#

this is what you wrote right

hushed tapir
#

Yes

twin anchor
#

okay perfect

#

yes this is true

#

now how can we manipulate this to relate to our goal inequality

hushed tapir
#

Idk how to do that

#

We gotta introduce z

#

I think

twin anchor
#

no we dont

#

just look at the LHS

#

our goal was to simplify it right

hushed tapir
#

Yes

twin anchor
#

and we said that (n^2 -1)/(3n^2) is smaller than (n^2 - 1)/(3n^2 - 1)

hushed tapir
#

Yes

twin anchor
#

if i subtract a smaller thing from the same number, whats the effect on the overall difference

hushed tapir
#

Huh?

twin anchor
#

you can figure this out

#

if $a < b$, then what's the relationship between $x-a$ and $x-b$

boreal girderBOT
#

snowflake

hushed tapir
#

x-a bigger

twin anchor
#

yes

#

and we can prove that from simple inequality rules, multiply by -1 on both sides and add x

#

so with that in mind, what does the inequality look like with 1/3 and our rational expression

hushed tapir
#

1/3 greater than our expression?

twin anchor
#

$\frac{1}{3} - \frac{n^2 - 1}{3n^2-1} < \frac{1}{3} - \frac{n^2-1}{3n^2}$

boreal girderBOT
#

snowflake

hushed tapir
#

Yes!

twin anchor
#

do you see why we care about doing this

hushed tapir
#

Not really

twin anchor
#

we wanted to show that the LHS was < ε right

hushed tapir
#

Yeah

twin anchor
#

what can we instead show now

hushed tapir
#

Um?

#

Something with our new fraction

twin anchor
#

instead of showing this directly

#

we can do something else that will prove this indirectly

twin anchor
#

think about transitivity of inequalities

hushed tapir
#

What’s transitivity of inequalities

twin anchor
#

if a < b and b < c then a < c

hushed tapir
#

But our new inequality is bigger, so how would that help

twin anchor
#

we know a < b, and we want to show that a < c

#

what do we have to show for that

twin anchor
hushed tapir
#

I feel so stupid, I’m really confused. I get the idea of using another inequity but idk how that applies here

twin anchor
#

okay, so we had our original quantity a (a is our 1/3 - fraction).

we want to show that it's smaller than this other quantity c (c is epsilon).

we found a new quantity b that's bigger than a (b is 1/3 - the new fraction).

if we can show that b is smaller than c, and we know that b is bigger than a, then a must also be smaller than c

#

right now, we know b is bigger than a, so all we need to do is show that b is smaller than c. if we can do that, then we've indirectly proven that a is smaller than c

#

and a < c is our goal

hushed tapir
#

Yes!

twin anchor
#

so what do we want to prove right now

hushed tapir
#

1/3 - new fraction is less than ε

twin anchor
#

perfect

#

in other words, we need to find n such that $\frac{1}{3} - \frac{n^2 - 1}{3n^2} < \epsilon$

boreal girderBOT
#

snowflake

hushed tapir
#

Yes

twin anchor
#

what are your ideas to do next

hushed tapir
#

Solve for n in terms of epsilon

twin anchor
#

right yes

#

how should we do that

hushed tapir
#

Make a new inequality?

twin anchor
#

(do you see how to solve from here)

#

no

#

we can solve from this one

#

what is the literal first step we can take right now

#

why was it helpful to get rid of that -1 in the denom

hushed tapir
#

Distribute

twin anchor
#

exactly

#

after doing that and simplifying, what do we get as our new equivalent condition for n

hushed tapir
#

But we are using something we are trying to prove

twin anchor
#

yes, distributing is a reversible operation

hushed tapir
#

No, I mean with the epsilon and stuff

twin anchor
#

so i know i can undo my steps once I can get to n

#

we haven't specified anything on epsilon yet

#

its fully arbitrary still

#

and our n is allowed to depend on epsilon

#

we're trying to prove that for all epsilon, there exists some n such that the inequality holds

#

so that n can intrinsically depend on the specific epsilon

#

our goal was to show that inequality right? if we can apply a series of reversible steps to reach a direct constraint on n based on the given epsilon, then for that epsilon, we can find a specific value of n and work backwards to show that the inequality holds

#

it might make more sense once we finish

hushed tapir
#

The inequality should be switched in the last step

twin anchor
#

n > right

#

that seems good to me

#

so after applying our reversible steps, we got that n should be > sqrt(1/(3ε))

#

because all of our steps were reversible, this means that if n > sqrt(1/(3ε)), then (n^2 - 1)/(3n^2) > 1/3 - ε, meaning that (n^2 - 1)/(3n^2 - 1) > 1/3 - ε, proving that the RHS isn't an upper bound

#

you can easily verify that this is true by proving this starting from n > sqrt(1/(3ε)). we just don't have to because all of our steps were reversible

hushed tapir
#

Huh

#

So we found an inequality satisfying n, so we using the transitive properties of inequalities to show that since n exists, then the inequality exists

twin anchor
#

we found an inequality describing the necessary conditions on n for our goal inequality to be true

#

and then yes, we showed the goal inequality through transitivity using our modified inequality

hushed tapir
#

One sec

#

Let me formulate this

#

So where from here

twin anchor
#

pick some integer n such that n > sqrt(1/(3ε))

#

then it follows that 1/3 - ε is less than that corresponding element of the set

#

that's basically it

hushed tapir
#

So what did that prove

#

In that since we found a condition for n, then 1/3 must be the sup

twin anchor
#

we proved that every number less than 1/3 isnt an upper bound

#

since you already showed 1/3 is an upper bound, that makes 1/3 the least upper bound

hushed tapir
#

Awesome

#

Thank you so much

compact pewterBOT
#

@hushed tapir Has your question been resolved?

#
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wheat seal
#

Help needed

compact pewterBOT
wheat seal
#

What do you mean by max value of x + y + z
When they are complex

compact pewterBOT
#

@wheat seal Has your question been resolved?

rotund sphinx
compact pewterBOT
#
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compact pewterBOT
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carmine garden
compact pewterBOT
carmine garden
#

wrong problem

#

my bad

mild sky
#

Well every element of H has odd order

carmine garden
#

well, how

mild sky
kind viper
#

order of element divides order of group

carmine garden
#

ah right

#

Lemme prove that

#

right

#

follows from the order of a group, divides the order of it's subgroups

carmine garden
#

oops yea

mild sky
#

Order of subgroup divides order of group

#

Brb

carmine garden
#

I'm not sure if it's 0 or infty here

mild sky
#

Infty

kind viper
carmine garden
#

right, I got confused

#

sorry

compact pewterBOT
#

@carmine garden Has your question been resolved?

carmine garden
#

so like if rotating by 90deg preserves symmetry we're done

kind viper
#

not every regular polygon survives a 90° rotation

#

it doesn't work for n=6

carmine garden
#

yeah I just realised what to do

kind viper
#

note that having a subgroup of order 4 isnt the same as having an element of order 4 -- the latter property is stronger!

carmine garden
#

We have each interior angle is $\frac{180 (n-2)}{n}$

boreal girderBOT
carmine garden
kind viper
#

why 3

kind viper
carmine garden
kind viper
#

a rotation of order 3 cannot possibly belong to a subgroup of order 4

carmine garden
#

now I can have the 180 deg rotation

#

that gives me a group of order 2

kind viper
#

a 180° rotation does generate a subgroup of order 2 indeed

carmine garden
#

I could then add a vertical and horizontal reflection

#

would that work

short ferry
carmine garden
#

yes

#

seems to work

short ferry
#

btw you are currently talking about a group generated by vertical refleciton, horizontal reflection and 180° rotation?

carmine garden
#

I have a n-gon

#

I'm looking at a dihedral group of order n where n is an even integer

#

And it's subgroups of order 4

short ferry
#

you had a group generated by 180° rotation (this one was of order 2)

#

and you wanna add vertical and horizontal reflection now?

#

That could add way more elements than you think

#

unless you intend to add only vertical and horizontal reflection, in which case you should recheck the definition of a group

carmine garden
short ferry
carmine garden
#

Same for a horizontal reflection

#

Ah I see what you mean

#

I see what you mean

short ferry
#

What do I mean then?

#

Can you tell what's wrong with your idea now?

carmine garden
short ferry
#

indeed

#

doesnt satisfy the closure axiom if that's how you call it

#

seems like you'll have to do a small tweak

mild sky
short ferry
carmine garden
#

I see what you mean

compact pewterBOT
#
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#
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wheat seal
#

How to do this

compact pewterBOT
wheat seal
#

I tried transferring 5 and 13 to other side

#

Then make a polynomial q(x)

#

= p(5x) + p(x) - 18

#

That didn't give any ideas

#

Can anyone give more strategies?

#

I also have a solution but I failed to understand
Can anyone explain that too?

rotund sphinx
#

Let $r$ be the integer root. Then, $$p(x)=(x-r)q(x)$$ for some polynomial $q$ with integer coefficients.

boreal girderBOT
#

Civil Service Pigeon

rotund sphinx
#

Further hint (this gives away a lot): It follows that ||10-r divides 5|| and ||2-r divides 13||

rotund sphinx
wheat seal
rotund sphinx
#

well I kinda need to see the solution to explain it

#

and you also need to be specific about what part you don't understand

wheat seal
rotund sphinx
#

and they give you p when x=2 and x=10

#

so it's natural to put in those two values

#

and at this point you see it and go

#

oh

#

question done sans number crunching

#

yay

wheat seal
#

Huh?

rotund sphinx
rotund sphinx
#

because 0 is generally nice to work with

#

not that it really matters

wheat seal
#

Wait a minute
So they are trying to make a polynomial just as I did?
What is the difference in their and my formation?

rotund sphinx
#

I explained their formation using the logic I used since they're basically identical

#

idk what your intuition was tbh

wheat seal
#

I mentioned it

wheat seal
#

Just make a polynomial that is 0 at 2

rotund sphinx
#

Ig you're trying to combine the conditions into one?

#

but a lot of the time you lose information that way

#

ex. Let's say you're given a=7 and b=5

#

then you know a+b=12

#

but if you now only work with a+b=12, you have now lost information

#

because you can no longer deduce the values of a, b with just a+b=12

wheat seal
#

Ok
A bit too complex

#

Nice then

#

How did they reduce r to +- 1 etc.

rotund sphinx
#

(r-2)q(r) = -13

#

q(r) is an integer because q has integer coefficients

#

aka you have two integers multiplying to -13

wheat seal
#

It's totally unimaginable for me
Why would you only use the p2 = 13

#

Yes

rotund sphinx
#

13 is more restrictive since it's prime

#

fewer possibilities for factors

#

so it's easier to narrow down with that first

#

before turning to p(10)

wheat seal
#

My vision is clearer

#

You idea was way smarter

#

It would make r restricted to only a multiple of something

#

Sorry not r
X

rotund sphinx
#

yeah this is a classic case of "do the easy stuff first because if it doesn't work, you didn't waste that long. but if it turns out to be the main idea and you glossed over it, well then you feel like shit"

#

the easy stuff being rewriting the condition as p(x)=(x-r)q(x) and plugging in the values of x corresponding to the given values of p

wheat seal
#

Right

#

Thanks

#

Bye

rotund sphinx
wheat seal
#

.close

compact pewterBOT
#
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foggy sandal
#

can somebody see if this proof is correct , if it has errors , where and how can i fix it please? Appreciated much.

chilly basalt
foggy sandal
#

sorry will do

chilly basalt
foggy sandal
weak cobalt
#

Why f,g continuous on I?

#

I know it's not the proof part but I don't think it's necessary, is it?

foggy sandal
#

I suppose its not neccesary as it will follow from them being differentiable.

weak cobalt
#

No, it does not at a

foggy sandal
#

True, i suppose it needs to be continuous at a for some reason, but im not sure what

weak cobalt
#

I don't think it needs to; anyway, it's probably irrelevant

foggy sandal
#

Yeah its just what it said in my book for the theorem

#

Oh actually i think i know why

#

I think its because to use the generalised mean value theorem in the proof, the function need be continous on the entire interval

weak cobalt
#

You sure? It says "f,g [...] are continuous on the open interval. So we can use the generalised mean value theorem..."

#

The open interval doesn't include a

#

Tbh I don't quite understand the proof

foggy sandal
#

Really which part

#

Pretty much what i said was

#

<@&286206848099549185>

kind crane
#

if you're just checking your proof, there are plenty of proofs online to check against

weak cobalt
#

I don't know if V is usual notation for what I assume to be a neighborhood; you might want to define it

#

Also the formula before the proof is missing an implies symbol

foggy sandal
#

Yeah theres not much standard notation for neighbourhoods, my book uses V but ive seen N and B before

weak cobalt
#

If I understand your proof correctly, it looks ok; but I'm not the best to ask

#

I'd follow riemann's advice

foggy sandal
#

Okay

#

I always have troubke verifying my proofs; im yet to find somewhere suitable or somebody to help

#

Do you have any advice

weak cobalt
#

No... I think verifying things is boring to most people, never mind proofs

#

And again I'm not the best to ask, sorry

#

It could be the case that some helpers would be willing and confident to review your proofs but they haven't stumbled upon your channels, idk

#

This is not a paid service after all

#

You might have more luck asking a professor in your university (or any nearby one if you aren't in uni)

compact pewterBOT
#

@foggy sandal Has your question been resolved?

compact pewterBOT
#
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pale tiger
#

i'm really confused on how to solve this problem. i'd assume they're asking for a 95% confidence interval, so i tried plugging it in to the formula, but how am i supposed to calculate a confidence interval w/ out the sample size (n)?

static timber
boreal girderBOT
pseudo willow
#

One message removed from a suspended account.

pale tiger
#

do i plug in the values of my mean and standard dev. into the second part of that

#

to end up with an inequality?

#

would that inequality be the interval?

pseudo willow
#

One message removed from a suspended account.

pale tiger
#

sry, im not actually taking stats rn, i have no idea what this means 😭

static timber
#

Yes! If a random variable follows a normal distribution, then the probability of its value being within 2 std. deviations of the mean is approximately 95%

kind crane
#

maybe you know it as empirical rule

pale tiger
#

ohhh

#

tysm!!

#

so then i'd end up w/

#

2708-3692?

#

and that's that?

kind crane
#

show all your steps

pale tiger
#

for the left side

#

3200-(2*246) =2708

#

and for the right

#

3200+(2*246)= 3692

#

?

kind crane
#

,calc 3200-2*246

boreal girderBOT
#

Result:

2708
kind crane
#

,calc 3200+2*246

boreal girderBOT
#

Result:

3692
kind crane
#

sounds right

pale tiger
#

k, thanks a lot!! have a nice day :))

#

.close

compact pewterBOT
#
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compact pewterBOT
#
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vivid wedge
compact pewterBOT
#
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
vivid wedge
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Around 2

compact pewterBOT
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Show your work, and if possible, explain where you are stuck.

vivid wedge
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Idk where to go from here in calculating the tension

twin idol
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Ooo a statics question

twin idol
signal willow
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Wait why are you multiplying 200 by 9.8

cold widget
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notice the unit

vivid wedge
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ohhh

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I see

cold widget
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so can you find out T3

twin idol
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Do you know how to relate the angles and the sides?

vivid wedge
cold widget
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show why is it the same if they are same

vivid wedge
twin idol
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Hmm

timid dune
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Start with T3, what do you think T3 equals?

vivid wedge
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I'm kinda clueless

vivid wedge
timid dune
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Yep

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Now let’s consider the forces acting on the intersection between the 3 lines

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What can you say about the forces acting in this point?

vivid wedge
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Is the net force 0 because it's still?

twin idol
timid dune
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But we need to get clear what exactly is experiencing 0 net force

vivid wedge
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The system as a whole?

twin idol
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Sure

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But we mean something between the 3 tension forces

vivid wedge
twin idol
vivid wedge
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Cables ? 😭

twin idol
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Well they are cables

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But what location makes T1 and T2 and T3 intersect?

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In the diagram

vivid wedge
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the beginning of T3 ?

twin idol
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Yea...

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Can you show where that is on the diagram?

vivid wedge
twin idol
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Now we know the system as a whole doesn't move

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But this point is important because it allows us to find the forces in T2 and T1

vivid wedge
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so that means T1 + T2 = -T3 right

twin idol
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Not quite

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Now do you remember the 2 equations of statics for stationary points?

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Hint: it's related to the x and y directions

vivid wedge
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fnetx = 0 and fnety = 0 ?

twin idol
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Yep yep

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Now we need forces in these directions to make use of these 2 equations

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But it appears that T2 and T1 are not in full x or y directions

vivid wedge
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do we take the sin and cos of each of them and find the direction with the pythagorean theorem

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of each one individually I mean

twin idol
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Yea

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sin and cos will come into play here

vivid wedge
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and since T1 is in the fourth quadrant it would be sin319 and cos319 ?

twin idol
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Wait

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No no it's not in the 4th quadrant when you inspect it from the point you highlighted

vivid wedge
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Oh it would be the second then

twin idol
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Ye

vivid wedge
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Okay but how exactly do I find the tension in the cable from that

twin idol
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You found the x and y components for T1 and T2?

vivid wedge
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is it just the sin and cos of the angles relative to the point ?

twin idol
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Ye

vivid wedge
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is that right

twin idol
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Yeah but don't forget that they're not only the sin and cos.
The sin and cos must be multiplied by a magnitude

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Namely T1 and T2 themselves

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T1x = T1 cos(131)

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Wait

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139

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T1x = T1 cos(139)
T1y = T1 sin(139)

vivid wedge
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why 139

twin idol
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180-41

vivid wedge
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I just did 90 + 41 to get the reference angle in the second quadrant

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is that wrong?

twin idol
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Sadly that is not correct

vivid wedge
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thank you for your patience btw

twin idol
vivid wedge
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Okay and how do I connect this to the tension in each of the cables

twin idol
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Draw a free body diagram

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Then use the statics equations

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And you'll find T1 and T2

vivid wedge
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Alright I think I can figure it out from here

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Thank you so much for your patience

twin idol
vivid wedge
twin idol
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If you need any help, the help channels are open

vivid wedge
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Okay thank you again

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.close

compact pewterBOT
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Channel closed

Closed by @vivid wedge

Use .reopen if this was a mistake.

compact pewterBOT
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smoky heart
#

wondering if anyone can help