#help-13

428200 messages · Page 483 of 429

sick ruin
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Overall, yeah

pale kiln
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Question a gives me two options tho

cedar kilnBOT
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pale kiln
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Oh

cedar kilnBOT
pale kiln
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Welp

sick ruin
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Yeah they’re asking “where is y increasing” (first box) and “where is y decreasing” (second box)

pale kiln
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Ohhh I see

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I see

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So

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The range of this in interval notation is

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Oh dang I was gonna figure the answer then ask

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Its aight

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The next question are similar

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And I can use your answer as reference

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Thank you

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Oh

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Aight one sec

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Give me one sec

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[2,4] U [4, infinity)

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Got it

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You there?

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Oh yo

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Ok

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Is my answer wrong?

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Ohh

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I see

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It says it was wrong tho

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Hmm

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One sec

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Oh

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Interesting

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Can I screen shot all of this?

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For future reference?

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Okay

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Im confused on another thing

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Its either 6

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Or -1

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But they say its neither

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Unless the answer is -6???

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Oh its 1

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I got it

cedar kilnBOT
#

@pale kiln Has your question been resolved?

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crimson sedge
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hey

cedar kilnBOT
crimson sedge
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how do i check the domain of this function

cedar kilnBOT
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@crimson sedge Has your question been resolved?

crimson sedge
#

<@&286206848099549185>

cedar kilnBOT
#

@crimson sedge Has your question been resolved?

cedar kilnBOT
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shadow scarab
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how does, ln x = 5 (e^5 = x) become e^ln x = e^5???

dense hornet
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by raising e to the power of "both sides"

shadow scarab
dense hornet
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it's just an informal way of expressing the step out in words

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basically, what they did here is they took one side of the equation, say, ln(x) and then raise e to the power of ln(x), you get e^(lnx), however recall that ln(x)=5, hence e^(lnx) is also e^5

shadow scarab
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ik about the right side. But i dont get how the left side become e^ln x

dense hornet
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hence we get the equation e^(lnx)=e^5

shadow scarab
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i see.

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but dont we have to do the thinbg on both sidces?

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sides*

dense hornet
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yeah, you can think of it as such

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hence like i have said

dense hornet
shadow scarab
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i see. Thx

#

.close

cedar kilnBOT
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tepid chasm
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I am answering a definite integral. I am left with 1/2(-ln3 - ln5). Up to how many decimal places should I use for ln3 and ln5? Or does it not matter?

jaunty mural
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You leave it in exact form

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Why would you use decimal places at this stage...

tepid chasm
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Aight, leaving it exactly as it is

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.close

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cinder tide
cedar kilnBOT
solid quarry
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thats a cool questionnn

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i think whichever goes last has an advantage

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that would be the odd numbered turns since 19^2 = 361

cedar kilnBOT
#

@cinder tide Has your question been resolved?

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solid quarry
#

.reopen

cedar kilnBOT
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solid quarry
#

hi

cedar kilnBOT
solid quarry
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is it ideal for the second player to mimic the first?

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in a way reflected about the diagonal

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then even if the first player plays a perfect game, each advance will be mimicked

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up until the final turn where the first player could get one more point

solid quarry
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is the first player bound to win if they just fill every cell they can with a 1?

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no, theyd have to put at least 19 0s to keep from tying

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@celest ledge halp

celest ledge
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What makes you think I am able to solve competition questions…😂

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I just happened to solve two , I generally can’t solve them at all

solid quarry
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u solved the chess one

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this one is also on a grid

celest ledge
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😂the chess one is definitely not a competition question

cedar kilnBOT
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@solid quarry Has your question been resolved?

misty crescent
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just was

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in vc

celest ledge
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Well, at least I can make Alice not lose now

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She puts all 1 for her places at first row, that gives her at least 10

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Then starting from second row.she places 1 when the above placed by bob is 0, she places 0 when the above is 1

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So sum of any column is at most 10

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I am substituting it to make it a Winning strategy

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Well seems like that’s how far I can go. I can only make Alice win or draw.

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If bob is smart then this way it’s definitely a draw

solid quarry
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im not sure i get it

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why must sum of every column be at most 10?

celest ledge
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It’s not necessarily that order they place numbers but the thought is still valid. Alice place 1 at (1,1). If bob place a number at first row then Alice places a 1 at first row. If bob places a number 0 at (x,y) Alice places a 1 at (x+1,y) when x is even, Alice places a 1 at (x-1,y) when x is odd. Similarly If bob places a number 1 at (x,y) Alice places a 0 at (x+1,y) when x is even, Alice places a 0 at (x-1,y) when x is odd.

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You see, after it’s done, (2k,y)+(2k+1,y) must be 1

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So the sum of each column is either 9 or 10

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And Alice put 10 1 at the first row, so A>=10, and B<=10

solid quarry
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does it matter if bob places in those spots before? even though that would lead allice to get more points in the first row

celest ledge
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? Then they just switch identity

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Bob becomes alice, it doesn’t matter

celest ledge
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Why don’t we just let Alice put 0 all the cases😂

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First Alice place 1 at (1,1). If bob place a number at first row then Alice places a 1 at first row. If bob places a number at (x,y) Alice places a 0 at (x+1,y) when x is even, Alice places a 0 at (x-1,y) when x is odd.

solid quarry
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oo

celest ledge
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It sounds like it gives Alice more winning chance but the result seems unchanged.we still have A>=10, B<=10

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Anyway I still use first way, at least bob has to calculate harder in his head to make it a draw😂

solid quarry
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i keep second guessing your logic

solid quarry
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placing vertically makes more sense

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im gunna sleep on it

celest ledge
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If bob place at (1,x) then Alice place at (1,y) for any x ,y

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And 9 or 10, not 19

cedar kilnBOT
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@solid quarry Has your question been resolved?

cedar kilnBOT
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crimson sedge
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Hi can anyone tell me how to find this
So, what I got as my solution is C(r+b-k+1, r) <- events where you obtain the first red ball
C(a, b) is a over b (binomial coefficient)
But in the solution, they seem to have C(r+b-k, r-1) somehow

crimson sedge
cedar kilnBOT
#

@crimson sedge Has your question been resolved?

crimson sedge
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<@&286206848099549185>

cedar kilnBOT
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@crimson sedge Has your question been resolved?

cedar kilnBOT
#

@crimson sedge Has your question been resolved?

honest vortex
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@crimson sedge

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is that the question

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number 2

crimson sedge
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Yeah

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2.a

honest vortex
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the probability of picking red is

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r/(r+b)

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right

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and it says without replacement

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so wouldn't it be

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r

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/

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((r+b) * (K * -1) )

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I may be very wrong

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which I probably am

crude pine
honest vortex
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that's a multiply

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bro please help

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It's not even my question

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yet I'd like to know

crude pine
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I know but why would you multiply it

honest vortex
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I put multiply because every time

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you take one out

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you don't replace

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right

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so then if k is the number of trials

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then I multiplied -1 by K

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so it would mean for K amount of trials there was 1 ball take away each time

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wait would the numerator be R-1

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because there is no replacement?

crude pine
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Yes i still dont understand why would you multiply

honest vortex
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would it be

crude pine
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I think its -(k-1)

honest vortex
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oh

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my friend says it would be this

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then equate it to K

crude pine
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In first step -0
In second step -1

crude pine
honest vortex
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yeah exactly

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so you can't have r - 1

crude pine
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Yeah yeah

honest vortex
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yeah we agree on that

crude pine
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r/((r+b)-(k-1))

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Am i wrong

honest vortex
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can you explain the -(k-1))

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I'm not too sure why

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I just want to know

crude pine
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On the first step there shouldnt be any missing ball-> 1-1=0

On second step there should be (r+b)-1 balls

2-1=1

honest vortex
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Ohhh okay

crude pine
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Maybe i am wrong but idk

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I think its true

honest vortex
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maybe I should try writing on pape

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r

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wait

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what am I doing

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bruh

crude pine
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Huh

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What

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1.st (r+b)
2nd (r+b)-1
3rd (r+b)-2
4th (r+b)-3

honest vortex
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yes

crude pine
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Thats why k-1

honest vortex
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so in theory it should be

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k - 1

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YES

crude pine
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Yeah

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We solve it

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Solved

honest vortex
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thank you bus

crude pine
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No problem also thank you too

crimson sedge
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Oh

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xD

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I now understand what the problem actually meant

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You were basically emptying the whole box full of balls

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By taking balls one by one

crude pine
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Yeah

cedar kilnBOT
#

@crimson sedge Has your question been resolved?

#
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sand ether
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Need help on this last part

cedar kilnBOT
sand ether
dire geode
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what kind of help

sand ether
dire geode
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did you do i, ii, and the first half of iii?

sand ether
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yup

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nvm thx

#

.close

cedar kilnBOT
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dense berry
#

what does a tetrahedron even look like

cedar kilnBOT
dense wing
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4 triangles together in 3D space

dense berry
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this is for yr 11 trig and we've never heard of a tetrahedron

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so one triangular base and three triangles for sides?

dense wing
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pyramid with triangle base

dense berry
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ohh

dense wing
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(Also... just goggle what a tetrahedron is)

faint dirge
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I prefer bong

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it's a much better search engine

dense berry
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so for 8a, do I need to find the centre of the base

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i'm so lost how the heck do i even start this

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all i know is that all triangles have side length x and angles of 60 deg

faint dirge
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ok so it's not actually that bad

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8b is easier than 8a I can't visualise shapes

dense berry
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i am stupid too it's okay

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i need like some 3d shape thingy

faint dirge
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just a sec

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I got it

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a is to the left, b is to the right

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so a is actually easier

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it's a right triangle

dense berry
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right

faint dirge
dense berry
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yeah mines is much worse ignore it

faint dirge
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so you know the hypotenuse is s, you can find the base side

dense berry
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how?

faint dirge
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it's the radius of an equilateral triangle

dense berry
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it's the what

faint dirge
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it will be a constant proportion based off the side length

dense berry
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i've never heard of this

faint dirge
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radius, distance from center to corner

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it's very obscure, used for annoying geometric stuff like this

dense berry
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i see

faint dirge
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usually you only have to use side length, but the other stuff has a name too

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flashbacks to the orthocenter, circumcenter and incenter of a triangle

dense berry
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i don't think i've heard of it (yr 11 remember) but i'm already dreading it

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i always did hate geometry

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can i make a wild guess that the angle would 45 degree?

faint dirge
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I have no idea, I have not tried any of these numbers

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but I doubt it

dense berry
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wait

faint dirge
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some basic trig and logic (cutting 60º in half gives you 30º) tells you the radius is s/sqrt(3)

dense berry
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i think i have an idea

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what the hell

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okay wait hear me out

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the green triangle here is isosceles right?

faint dirge
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yup

dense berry
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therefore the two nonright angles are 45 right?

faint dirge
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nope

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because the center angle is not right

dense berry
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it's not?

faint dirge
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nope

dense berry
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dang

faint dirge
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it's 120º iirc

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anyways, we already got it

faint dirge
dense berry
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it's just that i want to apply stuff i already know

faint dirge
# faint dirge

so now we have two sides of this triangle, the hypotenuse and the adjacent (S and S/sqrt(3) respectively)

dense berry
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so anything involving sin rule, cos rule or the such

faint dirge
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this is all done using trig

dense berry
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but i don't know how to use them

faint dirge
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trig is the idea that for any angle, triangles must follow certain ratios

dense berry
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ohh

faint dirge
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if you take two right triangles, both with angle 38.38º, the opposite side divided by the hypotenuse is the same as in any other (right) triangle's opposite side divided by the hypotenuse

dense berry
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okay yeah i get that

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same ratios and such

faint dirge
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you can expand trig to nonright triangles, through the law of sines or cosines, but it's a pain P:

dense berry
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yeah i agree

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one second i'll brb

faint dirge
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if you do the math, you get a=S/sqrt(3)

dense berry
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wait wait can i try a different approach

faint dirge
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you can try

dense berry
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uh what the fuck

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i got (in my CAS) that x=b

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oh wait i'm a dumbass

faint dirge
# faint dirge

anyways, given our base side here is S/sqrt(3), and the hypotenuse is S, then cos(angle) will equal S/sqrt(3)/S = 1/sqrt(3)

dense berry
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the angle is 30 not 60

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i got it

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i think

faint dirge
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tell me when you find 8a then lol

dense berry
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is it 54.74 degrees?

faint dirge
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yup

dense berry
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it issss

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yeaaaaaaaasssss

faint dirge
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:D

dense berry
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wooohoo

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god that was a pain

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so this is what i did

faint dirge
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the other one's process is basically identical, dw (or maybe do worry?)

dense berry
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i probably should

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i used the sine rule

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so x/sin(120 = b(the base of the blue triangle)/sin(30)

faint dirge
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well.... yes

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you could have simply used trig the way it was originally created to be used, but this works perfectly fine too lol

dense berry
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i just found the other method

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...hard to digest?

faint dirge
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wdym?

dense berry
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like it didn't sit right with me

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i don't really know

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this makes more sense to me in a weird way

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but anyway

faint dirge
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oh yeah dw about it

dense berry
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now how do i go about 8b?

faint dirge
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if your method works, and you understand it, that's fine

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it's just an atraditional method

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so now we need the center angle

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we are going to do the exact same process

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we will find the base side, and the hypotenuse

dense berry
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wait which angle

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hang on hang on

faint dirge
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the angle between the front facing face and the base face

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the dotted line is meant to be vertical

dense berry
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oh

faint dirge
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but as you can see, I am not an artist

dense berry
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wait that's it?

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dang i really lost myself

faint dirge
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lol

dense berry
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i thought it was the angle at the top of the two sloping sides

faint dirge
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instead of using the radius (a)

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we use the "h" value as our base

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you can find that however, there are three easy methods

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law of sines, normal trig, or special right triangle memorisation

dense berry
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wait wait

faint dirge
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in order of how hard they are, starting with the hardest

dense berry
#

just a second please

faint dirge
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no worries

dense berry
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is it the yellow or the red angle i'm trying to find

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oh wait

faint dirge
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red angle

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the yellow angle is just 60º

dense berry
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yeah it's red i'm just dumb

faint dirge
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so, we want the hypotenuse, which is the distance from the center of the base of the triangle to the opposite point/angle

dense berry
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right

faint dirge
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then we find the ratio and take the arccos of that ratio, giving us our angle

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easy peasy

dense berry
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hang on

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i'm slowwwlly processing this

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3d shapes is so much pain

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so

faint dirge
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mhm

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which is why we reduce it to 2d projections and shapes

faint dirge
# dense berry

this is the 2d projection we use to understand what we need to find

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and to find those sides we need, we just use 2d triangles

dense berry
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right i think i got it

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and i need to find the height of the green tringle

faint dirge
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yup

dense berry
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*30 degrees for the angle not 60 🤦‍♂️

faint dirge
#

mhm

dense berry
#

soo

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73.22 degrees?

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dang it no it's not

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WHY THE HECK IS IT NOT

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i'm going to die here

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okay okay

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finally

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oh my god FINALLY

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i got it i hate trig i hate geometry i hate maths

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thanks so much sycthe for ur help if u see this

#

.close

cedar kilnBOT
#
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unborn hound
cedar kilnBOT
unborn hound
#

kinda stuck here

#

not sure where to go next

cedar kilnBOT
#

@unborn hound Has your question been resolved?

unborn hound
#

.close

cedar kilnBOT
#
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hybrid orbit
#

how can i find the standard deviation and the mean when im only given the z score

hybrid orbit
#

i tried doing the let x thingie but it ended up just cancelling each other out

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this formula

dense wing
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you can't find both with only 1 z-score

hybrid orbit
#

this is where im confused with lol

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idk if the SD should be given but usually it is lol

dense wing
#

$Z\sim N(0,1)$

wraith daggerBOT
dense wing
#

if $X\sim N(\mu,\sigma^2)$, then $\frac{X-\mu}{\sigma}\sim N(0,1)$

wraith daggerBOT
hybrid orbit
#

what i did was
-2.37 = (.0089 - u ) / o
o = (.0089 - u) / -2.37

#

then plug that in the original equation but yeah it just cancelled out lol

dense wing
#

where the hell is .0089 coming from?

hybrid orbit
#

the z table

dense wing
#

Post your N(0,1) table

hybrid orbit
#

N(0,1) ?

dense wing
#

The standard normal.

hybrid orbit
#

Negative Z score table Use the negative Z score table below to find values on the left of the mean as can be seen in the graph alongside. Corresponding values which are less than the mean are marked with a negative score in the z-table and respresent the area under the bell curve to theContinue Reading

#

i just use this lol but our teacher makes us round it off to 4 decimals

dense wing
#

so yeah, 1/2-0.00889

hybrid orbit
#

oh 1/2 cuz its the mean?

dense wing
#

cause you want the area b/w 0 and -2.37

#

cause $P(Z\leq 0)=\frac{1}{2}$

wraith daggerBOT
dense wing
#

again, where $Z\sim N(0,1)$

wraith daggerBOT
hybrid orbit
#

wait wheres the zero from

dense wing
#

the mean of Z is 0

hybrid orbit
#

the problem is between mean and -2.37

dense wing
#

the variance is 1

#

yeah

#

it's a N(0,1) rv

hybrid orbit
dense wing
#

Z is standard normal....

#

so yes

#

the standard normal has the standard normal mean and variance

hybrid orbit
#

wait so if the mean isnt given we just assume it is 1 in normal distribution?

#

i mean 0

dense wing
#

You're told the curve is the standard normal

#

Thus you know it's centered at 0

hybrid orbit
#

ohhh

#

i see

#

its only zero if it is in standard

#

i get it now lol

dense wing
#

no

#

converse

#

if it's standard normal, the mean is 0

hybrid orbit
#

The standard normal distribution is a normal distribution with a mean of zero and standard deviation of 1

dense wing
#

you can easily have $N(0,2)$, which has mean 0 but not be the standard normal

#

yes

wraith daggerBOT
dense wing
#

$N(\mu,\sigma^2)$ has mean $\mu$ and variance $\sigma^2$

wraith daggerBOT
hybrid orbit
#

so if im looking for the area between
i use
1/2 - z score

if its to the right or left
1 - z score

dense wing
#

Don't try and make this into formulas.

#

Just use properties of the normal density function.

#

It's symmetric about the mean, area under it over all of R is 1

#

You just use logic about what the region you're looking for is like, and solve based on your table

hybrid orbit
#

Thanks!!

#

ill look into the properties lol

dense wing
#

Only proper rule you should remember is 68-95-99.7 rule imo

hybrid orbit
#

.close

cedar kilnBOT
#
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warm vector
cedar kilnBOT
warm vector
#

We’re finding x degrees here

livid hound
#

what have you tried so far

warm vector
#

I tried using the polygon formula

#

Ok I got it

#

Thanks

#

.close

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bold hinge
#

How much does a circular sector deviate from a triangle

bold hinge
#

In terms of area

cedar kilnBOT
#

@bold hinge Has your question been resolved?

cedar kilnBOT
#

@bold hinge Has your question been resolved?

astral crown
#

can't you calculate the difference

#

in terms of the angle

bold hinge
#

i could but that's not satisfying

#

i want to do it in terms of differentials

astral crown
#

so you're looking at something like the proof involving polar integration

bold hinge
#

proof of what? that a triangle deviates from a sector?

#

lol

bold hinge
astral crown
#

its something along the lines of area bound by a polar curve can be approximated using triangles or sectors

#

triangles will have like 1/2 r^2 sin(theta) and sectors will use 1/2 r^2 theta

bold hinge
#

really?

astral crown
#

but the approximation is better ofc for smaller theta

bold hinge
#

so this just becomes sin(theta) - theta

bold hinge
astral crown
#

yea, its the sum of many smaller triangles/sectors

bold hinge
#

or i guess 180 degrees

cedar kilnBOT
#
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scenic pasture
cedar kilnBOT
scenic pasture
#

how to do part b

flint plinth
#

if you plug in $e^{i\theta}$ to the formula for the series from part (a), what do you get?

wraith daggerBOT
#

OurBelovedBungo

scenic pasture
#

i get (e^itheta - e^(n+1)itheta)/1-e^itheta

flint plinth
#

looks right

#

ok now notice that the sine series is the imaginary part of the exponential series

#

so you need the imaginary part of your formula

scenic pasture
#

oh ok

#

ok thanks will see what i get

#

how do i get just the imaginary part since the denominator has e^itheta

#

so wont all of it be imaginary

flint plinth
#

one general approach is that if you have a complex number $w$, then its imaginary part is $\frac{w - \overline{w}}{2i}$, you could apply that to $w = \frac{e^{i\theta} - e^{i(n+1)\theta}}{1 - e^{i\theta}}$ and simplify

wraith daggerBOT
#

OurBelovedBungo

cedar kilnBOT
#

@scenic pasture Has your question been resolved?

#
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scenic pasture
#

Thanks for the help

cedar kilnBOT
#
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errant palm
#

pls help me

cedar kilnBOT
errant palm
#

nvm

#

i got it

cedar kilnBOT
#

@errant palm Has your question been resolved?

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slender flower
#

@livid hound

cedar kilnBOT
slender flower
#

whats the solution of the semi

livid hound
#

apply formula for area of a semicircle

slender flower
#

where>?

#

so y is 0?

livid hound
#

wdym

slender flower
#

y=sqrt(16-x^2)

livid hound
#

that's the equation of a semi-circle (arc)

slender flower
#

then?

#

whats next?

#

I thought x is 4

livid hound
#

wdym

slender flower
#

whats next?

livid hound
#

do you understand that you're being asked for the area of the shaded region

slender flower
#

IDK

#

can you show me what the solution >?

livid hound
#

we're getting there...

#

you first need to understand the problem

slender flower
#

then

#

so 8 is the x ?>

#

@livid hound

livid hound
#

whut

#

wdym by "is the x"

slender flower
#

can you show me how ?

livid hound
#

forget about the graph

#

for a sec

#

do you know the formula for the area of a circle?

slender flower
#

A=πr2

livid hound
#

use ^ to denote exponentiation

#

and hence what would be the area of a semi-circle

worthy snow
#

||A/2||

slender flower
#

1/2

#

1/2 πr^2

livid hound
#

$A_{\text{semi-circle}} = \frac12 \times \pi r^2$

wraith daggerBOT
#

ℝamonov

livid hound
#

can you identify the radius of your semi circle?

slender flower
#

4?

livid hound
#

yes

slender flower
#

then?

livid hound
#

well you have the formula for the area of a semi-circle

#

and you have the radius of your semi-circle...

slender flower
#

whats next ?

livid hound
#

use your radius and the formula

slender flower
worthy snow
#

sub in the radius to the formula to find the area of the semi circle

livid hound
#

the formula for the area of a semi-circle

#

that you just gave me

#

because that's what you have in your question

worthy snow
#

ramonov u mind helping me after this (#help-12)

slender flower
#

y=sqrt(16-x^2)

#

this one ?

livid hound
#

no

slender flower
#

oh I see

#

Wait

livid hound
#

that's what was supposed to be the equation of the curve

slender flower
#

pie r^2 ?

livid hound
#

no e in pi

#

pi r^2 gives the area of a full circle

#

1/2 * pi * r^2 gives the area of a semi-circle

1/2 πr^2
the formula for the area of a semi-circle
that you just gave me

slender flower
#

6.28

livid hound
#

how are you getting 6.28

slender flower
#

1/2 x 3.14 x 4

livid hound
#

you're not applying the formula properly

#

specifically you ignored the part where radius is squared

#

and you shouldn't be using an approximation for pi

slender flower
#

How?

#

wait

livid hound
#

$A_{\text{semi-circle}} = \frac12 \times \pi r^{\red{2}}\neq \frac12 \times \pi r$

wraith daggerBOT
#

ℝamonov

livid hound
#

$\pi \neq 3.14$

wraith daggerBOT
#

ℝamonov

slender flower
#

25.12

livid hound
#

leave pi as pi unless otherwise stated

slender flower
#

8 pi

#

i see

#

@livid hound

#

thats only the solution ?

tribal drum
#

1/2(pi r^2)

#

r is 4

#

1/2(pi 4^2)

livid hound
#

dunno what else you want

tribal drum
#

1/2 (pi 16)

livid hound
#

the question asks for the area of the region,
and you found it

slender flower
#

ok thanks

tribal drum
worthy snow
# tribal drum

dont write it like that, preferably if you keep the pi in the equation of the area

tribal drum
cedar kilnBOT
#

@slender flower Has your question been resolved?

cedar kilnBOT
#
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golden geode
cedar kilnBOT
golden geode
#

what wrong did i do

cedar kilnBOT
#

@golden geode Has your question been resolved?

golden geode
#

<@&286206848099549185>

inland tartan
# golden geode <@&286206848099549185>

gonna try help on this one because i was listening to https://www.youtube.com/watch?v=3YDOZjrVMAY when i saw this

Provided to YouTube by Sony Music Entertainment

Couch Potato (Parody of "Lose Yourself" by Eminem) · "Weird Al" Yankovic

Poodle Hat

℗ 2003 Volcano Entertainment III, L.L.C.

Released on: 2003-05-20

Composer, Lyricist: Jeffery Bass
Composer, Lyricist: Marshall Mathers III
Composer, Lyricist: Luis Edgardo Resto
Lyricist: Al Yankovic
Drum Prog...

▶ Play video
#

your handwriting's a little weird, no offense. can you tell me the actual question?

#

i can explain the question and you can double check your working as we go along

golden geode
#

lol none taken stress taking over

#

hold one let me get it

#

question a

inland tartan
#

here's me solving the turning point, which you incorrectly calculated as (2,3)

#

what i'm doing here is finding the turning point of the original quadratic (x^2-4x+3), and then finding the minimum through completing the square (hope you know that), and taking the absolute value of the Y coordinate. i do this because the absolute value just makes the negative points positive (see the pic i posted of the 2 graphs)

#

you've factorised and found the "roots" (points where y=0) correctly though - just factorise the quadratic, and find when it's equal to 0

#

does the turning point/minimum solution make sense @golden geode ?

golden geode
#

hold up i am still kinda new to this topic

#

hw you got this

#

ohhh i got it thanks

inland tartan
# golden geode

basically, you can complete the square to find the minimum of a turning point - it's a little long so i can link you a video

inland tartan
golden geode
#

yep

inland tartan
#

aight nice. tell me if you need anything else

#

if you don't you can close the channel with .close

golden geode
#

thanks alot

inland tartan
#

np!

golden geode
#

.close

cedar kilnBOT
#
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lament flint
cedar kilnBOT
lament flint
#

i dont understand the solution

bold hinge
#

You should know this polynomial to be special

lament flint
#

how is it special?

bold hinge
#

(x^3 + 1) = (x^2 - x + 1)(x+1)

#

The solutions to this are the 3rd roots of 1

lament flint
#

yea

#

but why does 6 divide k

bold hinge
#

,w ((1+isqrt(3))/2)^3

lament flint
#

its sqrt(3)

bold hinge
#

Huh I can't read sorry

wraith daggerBOT
lament flint
#

should it be 3, since theyre cube roots

#

oh

#

theyre cube roots of -1

bold hinge
#

My bad

#

Yeah so that hopefully clears things up

#

3×2=6

lament flint
#

also why does 1-e = 1/e?

#

is that just by trying 1/e with the roots

bold hinge
#

1-x = 1/x
x-x^2 = 1
x^2-x+1=0

lament flint
#

oh

bold hinge
#

Yep.

lament flint
#

ok ty

#

.close

cedar kilnBOT
#
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bold hinge
#

👍🏻

cedar kilnBOT
#
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karmic totem
#

Hello! I am currently following a paper on physics simulation for a hobby project and I have come across a problem:
Given two vectors $v$ and $x = r \cross v$, I need a 3x3 matrix with the following property: $mv = x = r \cross v$.
If I remember correctly, one cannot simply divide two vectors and expect to get the right matrix (I wouldn't know how to anyways). So which strategy would one use to calculate the needed 3x3 matrix?

wraith daggerBOT
cedar kilnBOT
#

@karmic totem Has your question been resolved?

karmic totem
#

<@&286206848099549185>

karmic totem
#

.close

cedar kilnBOT
#
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scenic crest
cedar kilnBOT
scenic crest
#

Why did definite integral of second function(1) become "x" and not "e-1" in 2 line of solution?

#

And also why did {(lnx)^n.x|^e 1} become "e-0"?

cedar kilnBOT
#

@scenic crest Has your question been resolved?

cedar kilnBOT
#

@scenic crest Has your question been resolved?

cedar kilnBOT
#

@scenic crest Has your question been resolved?

cedar kilnBOT
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toxic flame
#

please can someone suggest which part needs simplifying

cedar kilnBOT
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cinder tide
cedar kilnBOT
celest ledge
#

I am about to use pigeonhole

#

We probably need to show that {Σ{x: x from A} mod (1+2+…+n)} contains 1+2+…+n different elements

terse roost
#

and you might be able to prove by recurence that there is a subset A of {0,...,n-1} such that every number between 0 and n(n-1)/2 is the sum of the elements of A

#

and i'm pretty sure you can do the same for A being a subset of {m,...,m+n-1} and dealing with numbers between m and n(n+m-1)/2

celest ledge
#

You mean n(n+2m-1)/2?

terse roost
#

By the way you would need m to be >= 1, m=0 doesnt work

#

between n(n+2m-1)/2 and m there are (n-1)(n+2m)/2 + 1 numbers if i'm not wrong. This is above 1 + ... + n if m>=1

#

then it's done if the recursive reasoning works

#

but it doesnt

#

my bad

celest ledge
#

Okay I got it. So we can prove his statement when m>=1

#

m=0 we know it’s false

terse roost
#

the recursive thing doesnt work

terse roost
#

yep

celest ledge
#

I proved it

terse roost
#

what if m = 5 and n = 2 ? you have 5 and 6 as numbers and want every numbers between 5 and 11 as sums. How do you build 7 ?

celest ledge
#

Shit

#

I thought I proved it

terse roost
#

what you can build are km + p(k) where p(k) can be decomposed as a sum of k elements between 0 and n - 1

celest ledge
terse roost
#

hum

#

maybe i have an idea

#

if we can prove that the km + p(k) all take different values mod n(n+1)/2 it would work right ?

#

then suppose they don't : km + p(k) = k'm + p(k') mod n(n+1)/2

#

there might be some way to find k'' and p(k'') that makes this work

celest ledge
#

That’s impossible I think

#

The former are 2^n -1 numbers

#

But the latter is (n+1)n/2

terse roost
#

what if m < (n+1)n/2 ?

#

plus its "mod"

cedar kilnBOT
#

@cinder tide Has your question been resolved?

terse roost
#

let's say km = m' mod n(n+1)/2 with m' between 0 and n(n+1)/2 - 1. The recursive thing works for m = 1 so there is q and p(q) such that p(q) = m' = km mod n(n+1)/2. Then there is p(n-q) such that p(q) = n(n+1)/2 - p(n-q) (p(n-q) contains the terms not use to build p(q)). There fore, p(n-q) = -m' mod n(n+1)/2 and km + p(n-q) = 0 mod n(n+1)/2. This means we just need to prove that it is possible to have n - q = k

cedar kilnBOT
#
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celest ledge
#

Got it, We need to have a q-subset whose sum =(n-q)m mod n(n+1)/2. But it seems transform back to our original question 😂

cedar kilnBOT
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crimson sedge
#

please help me

cedar kilnBOT
celest ledge
#

Infinity many

#

Or you want them to be what? Positive? Non-negative?

crimson sedge
#

yess

celest ledge
#

C(19,3) all positive solutions, C(23,3) all non-negative solutions

crimson sedge
#

but i need the even number of it

celest ledge
#

All them need to be even?

#

Positive or non-negative?

crimson sedge
#

yess

#

non negative and even

celest ledge
#

C(13,3)

crimson sedge
#

how?

celest ledge
#

It’s the same as 4 non-negative integers whose sum is 10

#

It’s equivalent to 4 positive integers whose sum is 14

crimson sedge
#

wait....

celest ledge
#

Put fourteen 1 on a line, use three objects to separate those 1 to create four blocks, it’s the same as choose 3 places to put those objects from 13 places

crimson sedge
#

how about there are both negative and positive?

celest ledge
#

So C(13,3)=286

crimson sedge
#

ohh

celest ledge
#

What?

#

A number can not be both positive and negative

crimson sedge
#

Ohhh....

#

Ok

#

.close

cedar kilnBOT
#
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real bone
cedar kilnBOT
real bone
#

Do I not have to use ln to calculate the derivative of 11^x -10^x?

kindred storm
#

@real bone Yes, but it's 11ˣ = eˣ ˡᵒᵍ⁽¹¹⁾.

real bone
#

Or did I forget the product rule

kindred storm
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So, you'll get log(11) eˣ ˡᵒᵍ⁽¹¹⁾ as the derivative, which equals log(11) 11ˣ.

real bone
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idk how you found that derivative

kindred storm
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I converted 11ˣ to eˣ ˡᵒᵍ⁽¹¹⁾ using the logarithm rules from algebra.

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Then I took the derivative of that.

real bone
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I actually don't remember that log rule

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Ok so

kindred storm
real bone
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Ty

kindred storm
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It's like rule 7 combined with an exponent rule.

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11ˣ = (11)ˣ = (eˡᵒᵍ⁽¹¹⁾)ˣ

real bone
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Rule 7 seems confusing

kindred storm
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Well, basically exponents and logarithms are inverses.

real bone
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Oh true

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B^k =logb of k

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Right?

kindred storm
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So, logₓ(xᵃ) = a and xˡᵒᵍˣ⁽ᵃ⁾ = a.

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No, log(bᵏ) = k log(b).

real bone
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Wait like if I wanted to make the inverse of b^k

kindred storm
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You have 11ˣ

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But that doesn't have a nice derivative rule.

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eˣ does, though.

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So, you want to change the base to e instead of 11.

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The way you do that is to move the 11 into the exponent.

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The way you do that is to do eˡᵒᵍ⁽¹¹⁾ ˣ.

wraith daggerBOT
#

Chai T. Rex

kindred storm
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You take the base whatever the new base is logarithm of the old base and put that in the exponent.

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So, if the new base is c, you take the base c logarithm of the old base.

wraith daggerBOT
#

Chai T. Rex

real bone
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Is that cuz x^logx is 1?

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Log base of x I mean

wraith daggerBOT
#

Chai T. Rex

kindred storm
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Never mind.

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Let's look at rule 7 again.

wraith daggerBOT
#

Chai T. Rex

kindred storm
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So, you can change the base from k to b using rule 7.

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Here's how you do it.

wraith daggerBOT
#

Chai T. Rex

kindred storm
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First, we parenthesize the 11.

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Then, we can use rule 7.

wraith daggerBOT
#

Chai T. Rex

kindred storm
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We've used rule 7 inside the parentheses.

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Does that make sense so far?

real bone
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Is log 11 the same as loge 11

kindred storm
#

log by itself usually means logₑ or ln.

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In calculus, I mean.

real bone
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Oh

kindred storm
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In other subjects, it can have a different base.

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Like in computers, it can have base 2 instead of e.

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But we're doing calculus, so it's usually base e.

real bone
#

Ok

wraith daggerBOT
#

Chai T. Rex

real bone
#

I forgot the rules of what the derivative of a logarithm is

kindred storm
#

Oh, it's a constant.

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log(constant) is a constant.

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Like log(5) is a constant.

real bone
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Which is zero

kindred storm
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So log(11) is also a constant.

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Well, let's be careful.

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For the derivative here, we use the chain rule.

real bone
#

Oh

kindred storm
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Because it's a function, eˣ, but with a different argument than x.

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Like if you have sin(10 x), that's like sin(x), but it's different than x.

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So, you use the chain rule.

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So, we do the chain rule.

wraith daggerBOT
#

Chai T. Rex

real bone
#

e^log(11)x * 1

kindred storm
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How did you get the 1?

real bone
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Derivative of the exponent

kindred storm
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OK, what's the derivative of log(11) x?

real bone
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Well I thought you said log of anything is a constant

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Oh

kindred storm
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Right, so it's a constant times x.

real bone
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Then it would be log(11)

kindred storm
#

Right.

wraith daggerBOT
#

Chai T. Rex

kindred storm
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And then we can work backwards on the e part.

wraith daggerBOT
#

Chai T. Rex

kindred storm
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So, we have log(11) 11ˣ.

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Does it make sense how we got that?

real bone
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Yes

kindred storm
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So, bˣ's derivative is log(b) bˣ.

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Which works when the base is e.

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log(e) eˣ = 1 eˣ = eˣ.

real bone
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But it's the same as taking ln of the function doing the derivative and multiply by the original function

kindred storm
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Well, if you have bˣ, it's the same as ln(b) bˣ.

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The derivative is.

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You can either remember to do the chain rule and the logarithm rules or you can remember the derivative of bˣ as log(b) bˣ directly.

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It's not the ln of the function doing the derivative, though.

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It's the ln of the base.

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So, bˣ means log(b).

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Does that make sense?

real bone
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Yea but log(b) is ln(b)

kindred storm
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Yes, in calculus it usually is.

real bone
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Well my original approach to the problem was to take the ln of function and find the derivative and multiply the result with the original function

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So if I did that why did I get the wrong answer

kindred storm
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With L'Hospital, you just take the derivative.

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You can't use the regular limit laws with things that are in indeterminate forms, like 0/0.

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They have restrictions on using them when certain things like that happen.

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So, you need to use L'Hospital or some other method.

real bone
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Yea but another way of finding a derivative of a function is the way I used

kindred storm
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Do you mean logarithmic differentiation?

real bone
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Yes

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So I took that approach to finding the derivative and got the wrong answer some how

kindred storm
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OK, let's try that.

real bone
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And thank you for showing me another way btw

kindred storm
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(11ˣ)' = 11ˣ (ln(11ˣ))'

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= 11ˣ (x ln(11))'

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= 11ˣ (ln(11) + 0)

real bone
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Yep

kindred storm
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= ln(11) 11ˣ.

real bone
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Oh

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I think I forgot product rule

kindred storm
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Oh, OK.

wraith daggerBOT
#

Chai T. Rex

real bone
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I will multiply by the original function after of course

kindred storm
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No, the first part is right, but the second and third parts aren't.

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You shouldn't get x ln(11) - x ln(10) in the top.

real bone
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xln(11/10)?

kindred storm
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Well, the first expression's limit is 0/0.

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Which is indeterminate.

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So, you can use L'Hospital's.

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But when we used L'Hospital's we got ln(11) 11ˣ - ln(10) 10ˣ on top, not those.

real bone
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I thought lhopital's just said to take a derivative of the numerator and of the denominator separately

kindred storm
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Yes, and then the new numerator is the derivative of the old and the new denominator is the derivative of the old.

real bone
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Did I mess up in applying the ln?

kindred storm
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No, you didn't write the result of the derivative.

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The result was 1 on bottom and ln(11) 11ˣ - ln(10) 10ˣ on top.

real bone
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Ok so applying ln was correct

kindred storm
#

You have x ln(11) - x ln(10), which is not the same as ln(11) 11ˣ - ln(10) 10ˣ.

real bone
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xln11 - xln10 all over lnx

kindred storm
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Why are you applying logarithm?

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The derivative is done.

real bone
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Logarithmic differentiation

kindred storm
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Yes, and we got ln(11) 11ˣ - ln(10) 10ˣ on top, right?

real bone
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I dodnt

kindred storm
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Well, we have (11ˣ)' = 11ˣ (ln(11ˣ))'.

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Where did you go from there?

real bone
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Cuz I was gunna do 1. Take ln
2. Take derivative
3. Multiply by original function

kindred storm
#

No, that's not how logarithmic differentiation works.

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It's not take the logarithm and then do the derivative.

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It's the original expression times the derivative of the logarithm of the original expression.

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f'(x) = f(x) (ln(f(x)))'

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Don't forget the f(x) in front, multiplied with the derivative of the logarithm.

real bone
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Yea I was gunna multiply by f(x) after

kindred storm
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OK, but then you can't write it all as one expression.

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You can't have x ln(11) - x ln(10).

real bone
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I'm still wanting to make sure I did ln(f(x)) correctly

kindred storm
#

You need to separate it out.

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It's better to write exactly what you're doing.

real bone
#

Ok like doing each step for each term separately?

wraith daggerBOT
#

Chai T. Rex

kindred storm
#

Yes, because you're taking the derivative of each term in the numerator.

real bone
#

Oh

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True ok

kindred storm
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Not of the whole numerator.

real bone
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So if we just deal with 11^x

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We do xln11 then find it's derivative

kindred storm
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Yes, but write out what you're doing so that it can be followed along with.

real bone
#

Ok

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So ln(11^x)

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Is xln11

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Then I do product rule and chain rule I think

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Erm not chain rule

kindred storm
#

Yes, the product rule is correct.

wraith daggerBOT
#

Chai T. Rex

kindred storm
#

See, here the left side tells what the right side, your work, means.

real bone
#

Product rule gave me ln11 + x/11

kindred storm
#

How did you get x/11?

real bone
#

Derivative of ln11

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Times x

kindred storm
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What's the derivative of ln(11)?

real bone
#

1/11

kindred storm
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No.

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ln(11) is a constant.

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,calc log(11)

wraith daggerBOT
#

Result:

2.3978952727984
kindred storm
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It's 2.40 and so on.

real bone
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Oh its it only ln/x that has the derivative of 1/x?

kindred storm
#

Right.

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It has to have a nonconstant variable.

real bone
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Ok my bad

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So ln11 + 0

kindred storm
#

Right.

real bone
#

And the same for 10^x

kindred storm
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Yes, but first finish (11ˣ)'

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Multiply the derivative of the logarithm with the original function.

real bone
#

11^x * ln11

kindred storm
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If you forget to do that, there's a way to remember.

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You just write what you're figuring out on the left.

wraith daggerBOT
#

Chai T. Rex

kindred storm
#

That way, you'll know you're not done yet when you get ln(11), because you don't have (11ˣ)' yet.

real bone
#

Oh ok

wraith daggerBOT
#

Chai T. Rex

kindred storm
#

And then do the part in parentheses on the right.

wraith daggerBOT
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Chai T. Rex

real bone
#

The bottom is just x/x

kindred storm
#

That way, you use the ' to keep track of what you differentiate.

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Sorry, keep track of what you still need to differentiate.

real bone
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So 11^x * (ln11) - 10^x * (ln10)