#help-33

1 messages · Page 230 of 1

queen sun
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If you wrote it back to equations you’ll see how it works

fervent rampart
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gauss-jordan requires about 50% more operations for large matrices

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and is also numerically unstable

queen sun
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What does that mean? Edit: I can search things up

fervent rampart
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so it's good for hand calculations (which use small matrices and precise fractions) but not suitable for computer algorithms

queen sun
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Floats be like: $0.1+0.2\ne0.3$

elfin berryBOT
#

BBMaths

elfin badger
queen sun
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Start from the bottom row and work backwards (it’s in the name “back substitution”)

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Like z=-1 then put that in the next row up and get y

elfin badger
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z doesnt equal that

fervent rampart
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the equation at the bottom is just z = -1

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so how could z not equal -1

elfin badger
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i was looking at the one above it

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the green one

fervent rampart
#

you do the back substitution process on the yellow one (since it's in REF)

elfin badger
#

.

queen sun
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-32z=32

fervent rampart
#

you could do it on the second to last one as well but then you get -32z = 32 which can still be solved for z

queen sun
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So z=-1

elfin badger
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oh

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so for y=

fervent rampart
#

to find y, you go to the next equation above, which is y + 3z = -1, and plug in the value of z you got previously

queen sun
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The green one is 2y+6z=-2 which will give the same answer it doesn’t matter which you choose, you could even switch back and forth between the different matrices here!

elfin badger
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oh ok

queen sun
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Only because they relate by row operations

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Since row operations are about keeping the same x, y and z solutions but changing the system of linear equations

elfin badger
#

.close

marsh citrusBOT
#
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marsh citrusBOT
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devout charm
#

Hi guys does this look correct? This is for conic sections and I use the matrice function on my calculator for it

queen isle
#

Did you already verify by hand? As in plug your x and y values in and find that the equation holds?

queen isle
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Do that. It's the best way to do so because you can do this without using some fancy technique. Just put it in your calc and see.

devout charm
#

Hmm much more simple thank u

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It was wrong btw gulp

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Thanks so much!!

queen isle
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yes it was

devout charm
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Do u have any idea how I might’ve done the matrices wrong?

queen isle
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If I'm not mistaken the first column is the given x, the second column is the given y, and what is the third column for?

devout charm
#

I’m not all too sure, when my teacher taught it she Included the column but it always was the same number in the examples

queen isle
devout charm
#

Gulp

queen isle
#

Alson in your written solution A and C seems to have disappeared.

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81-36

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How did you get the fourth column?

devout charm
#

It’s a^2 + b^2

queen isle
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Beyond the verifying by hand I am of no help here since I never used a calculator for this purpose. Sorry. You should call for other helpers.

devout charm
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Ah, I understand. Thank you for the help regardless

queen isle
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Btw it's not 81-36

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(-6)^2 =36

devout charm
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Oh my god 😭

queen isle
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same for the 81-16

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Your mistake is likely that

devout charm
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Should’ve learned my algebra rules probably

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Went straight to calculus instead

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AH THAT WAS UT

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THANK YOU WAHAHAHAHA

queen isle
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Make sure though.

devout charm
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Yes! Will verify

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.close

marsh citrusBOT
#
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marsh citrusBOT
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quaint arrow
marsh citrusBOT
quaint arrow
#

i need help on b. i used a hessian calcualtor online and i can easily see that not all of the entires of the hessian will be positive

marsh citrusBOT
#

@quaint arrow Has your question been resolved?

quaint arrow
#

<@&286206848099549185>

marsh citrusBOT
#

@quaint arrow Has your question been resolved?

quaint arrow
#

<@&286206848099549185>

#

thank you for the response. this makes sense to me, but the directions say to use the second-order definition of convexity

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thank you so much for the response. I understand most of it. But i think i am slightly confused on differentiating matrices. Specifically, how did you go from 2·a(s)·w -> 2·a(s)·I + 4·a'(s)·w wᵀ?

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im sorry, i'm having a bit of trouble doing product rule. did i set u v improperly?

quaint arrow
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@chilly valley thank you so much for your help

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you really helped! Have a good day mate

#

.close

marsh citrusBOT
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past thicket
marsh citrusBOT
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hard laurel
#

If a sequence is bounded and it is converges to A then every subsequence of this sequence will Converse to A

hard laurel
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I guess it is true

stoic saddle
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where is question

wary kite
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i mean why do we need it being bounded

hard laurel
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Actually i am reading some notes

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So doubt arises in mind🙈

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We need to be bound otherwise we can't say anything

wary kite
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no?

hard laurel
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(-1)^n

wary kite
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that doesn’t converge

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it’s just redundant

hard laurel
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ohh wrong example

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Hmm

wary kite
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no need to mention it

stoic saddle
hard laurel
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n^2

wary kite
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that’s not bounded and diverges

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if it converges then it’s bounded

hard laurel
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I didn't write these notes. I am reading coaching notes

wary kite
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no need to mention it being bounded

hard laurel
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Let me show you hang on

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7 point

wary kite
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this is not what you said before

hard laurel
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They also mentioned bounded?

wary kite
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saying "and it converges"

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is not the same here

hard laurel
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Ohh my bad sorry

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Iff?

wary kite
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saying it’s a bounded sequence is a preliminary assumption

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also what is cps

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are you trying to prove 7 btw?

hard laurel
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Yeah

hard laurel
wary kite
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have you tried either direction?

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one direction is very trivial

hard laurel
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Wdym?

wary kite
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proving either direction

hard laurel
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I don't need to prove just need to understand

wary kite
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same thing

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perhaps you don’t understand subsequences?

hard laurel
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subsequences is part of sequence

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so sequence is converges to L then all points are travelling to that limit slowly

wary kite
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why slowly?

hard laurel
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Subsequences will also travel in that direction

wary kite
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what do you mean by slowly

hard laurel
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nothing specific

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Slowly fast

wary kite
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🤔

hard laurel
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I mean points which is very close to that limit can be Faster

wary kite
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closer = faster?

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i’m not sure i follow sir

hard laurel
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Nevermind my words

wary kite
# hard laurel so sequence is converges to L then all points are travelling to that limit slowl...

think back to the definition of convergence. it requires that regardless of the distance from the limiting value, beyond a certain point eventually all of the sequence members will be within that distance from the limiting value. now since any subsequence you choose "extends" into this tail part of the sequence where all of the sequence members are hanging around the limiting value, we can just as easily say this subsequence also converges to the limiting value because it’s also in those neighborhoods

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does this make sense?

hard laurel
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yeah makes sense but please write more in simple English

wary kite
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i didn’t use big words

hard laurel
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If I have a bounded sequence

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I can't say it is convergent

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(-1)^n

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we have two limit points

wary kite
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ok sure what’s your point?

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notice that we can find two subsequences that don’t converge to the same value

hard laurel
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So for convergent we need unique limit?

wary kite
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take one subsequence to consist of the even terms and one to be of the odd terms

hard laurel
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If the sequence is convergent then what can we say about convergence of subsequences

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This is my doubt

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I mean each and every subsequence is converging so they will Converse to the same limit am I right

wary kite
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they don’t lie in the same neighborhoods but together they form the entire sequence and since they don’t hang out in the same neighborhoods the entire sequence certainly doesn’t converge because it needs all of its homies in one place

wary kite
hard laurel
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I am asking in rerverse

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My doubt is about subsequences

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1/n...it converse to 0

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if I take finite subsequnces

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1,1/2,1/3

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is this converging to 0?

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I'm sorry my doubt is messy and not clear

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Maybe i am mixing lots of unfruitful things

wary kite
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subsequences are not finite lists

hard laurel
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I see. They need to be infinite?

wary kite
#

they are sequences within the sequence

hard laurel
#

Great!!

wary kite
hard laurel
#

Hmm

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Thanks

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I got it

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.close

marsh citrusBOT
#
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hearty dust
marsh citrusBOT
hearty dust
#

is the ans to both just that f(x) and g(x) that they are continuous for which those statements hold

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that seems too short of an ans

marsh citrusBOT
#

@hearty dust Has your question been resolved?

hearty dust
cunning fiber
#

That’s the main thing

hearty dust
#

great tysm

#

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marsh citrusBOT
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near elbow
#

guys, i dont understand f and h

marsh citrusBOT
near elbow
#

for f, isnt Central Limit Theorem only applied when n is large and when distribution is unknown?

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and for h, why is it false?

marsh citrusBOT
#

@near elbow Has your question been resolved?

hearty dust
#

i dont think f and h are even related to central limit theorem

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those equations are related to the distribution of a sample population

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another helper can mistake me if im wrong

near elbow
#

alrightt thankyouuu

hearty dust
#

ye no worries

marsh citrusBOT
#

@near elbow Has your question been resolved?

hearty dust
#

bro wut 😭

marsh citrusBOT
#
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still temple
marsh citrusBOT
still temple
#

Find domain

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Shud i convert x to given, or given to x?

proud basin
#

what?

patent sandal
still temple
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[-1 ,1]

patent sandal
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so then what is the interval in which |x-1| lies

still temple
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Uhh

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How do i do

patent sandal
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think about it

still temple
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2 less than or equal to x and x less than or equal to 0?

patent sandal
#

yeah pretty much

still temple
#

Shud i switch signs if i apply mod?

still temple
patent sandal
still temple
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Ans is given opposite to what i got

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How?

patent sandal
#

whats the answer

still temple
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[0,2]

patent sandal
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its just what you said

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i mean thats just the proper way of writing it

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cus if you say 2<=x<=0 that means 2<=0

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which isnt true

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so you write 0<=x<=2

still temple
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Oh

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2cos inverse of 2x + sin inverse of x

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How to find for this?

patent sandal
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try it for yourself once

still temple
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Btw

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Will 2 in front of cos inverse of 2x affect domain?

patent sandal
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yes

still temple
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Oh

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Ok ill try

patent sandal
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if you meant the 2 in 2x

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then it will affect the domain

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the 2 of 2cos-1 2x doesnt

still temple
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So coeff has no effect?

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Ok

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[-1/2,1/2]

patent sandal
#

correct

still temple
#

,rccw

elfin berryBOT
still temple
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In this

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I get [-1,0]

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But ans is [-1,1]

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How so

patent sandal
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because its x^2

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if x is negative then (-x)^2 = x^2

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so its symmetric

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(-1)^2 = (1)^2 = 1

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(-1/2)^2 = (1/2)^2 = 0.25

still temple
#

No

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But here it is given as

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-x², not (-x)² right?

patent sandal
#

alright

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even so

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-x^2 = - (-x)^2

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so - (1/2)^2 = - (-1/2)^2 = -0.25

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-(1)^2 = - (-1)^2 = -1

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basically we have that -1 < -x^2 < 1

still temple
#

Wait wait

still temple
patent sandal
#

oh the minus sign became a bullet

still temple
#

Oh

still temple
patent sandal
#

so -1 < -x^2 < -1 then -1 < x^2 < 1 then -1 < x < 1

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i skipped a step, should i elaborate that?

still temple
#

But for +x², doesnt -1 become 0 since x² always greater than or equal to 0

patent sandal
#

since 0<x^2<1

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x must be between -1 and 1

still temple
#

Oh

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If the question is given as x²

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Is it [0,1]¿

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The hell is this?

#

.close

marsh citrusBOT
#
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marsh citrusBOT
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near elbow
#

guys i dont get the question of 1b

marsh citrusBOT
near elbow
#

this is 1a

spark otter
#

what's the probability that the confidence interval doesn't contain the actual population mean, and in fact the population mean is bigger?

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so P(mean > 13.0)

marsh citrusBOT
#

@near elbow Has your question been resolved?

near elbow
#

thats 0.005

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i was thinking of 0.01 but since it should be bigger than 13.0 then it is 1/2 of 0.01

near elbow
marsh citrusBOT
#

@near elbow Has your question been resolved?

tough sapphire
#

"...confidence interval will be below the population mean."

marsh citrusBOT
#
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compact crescent
marsh citrusBOT
compact crescent
#

.close

marsh citrusBOT
#
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stoic saddle
#

step 0 is to take off that literal fucking HITLER PFP. <@&268886789983436800>

weak surge
#

my man what is that pfp 💀

oak oxide
ruby mulch
#

But why the question is also closed?

stoic saddle
#

op closed it irrespective of the hitler-wannabe that showed up.

ruby mulch
#

Hell, even a blank pfp is better than that pfp

calm harbor
marsh citrusBOT
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rich isle
#

if i(n,a) =(1-2x)^(a-1)(x-x^2)^(n+1)/(n+1)+2(a-1)i(n+1,a-2)/(n+1) where i(n,a)=\int (x-x²)^n (1-2x)^a dx find i(14,28)

rich isle
#

i used various sources and got it as-

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$\frac{(28!)^{2}}{57!}$

elfin berryBOT
stoic saddle
#

can you send a picture or write what this i(n,a) thing is in proper LaTeX please

rich isle
#

if $$I(n,a) =\frac{(1-2x)^{a-1} (x-x^{2})^{n+1}}{n+1}+\frac{2(a-1) I(n+1,a-2)}{n+1}$$ where $$I(n,a) = \int_{0}^{1} (x-x^{2})^{n} (1-2x)^{a} dx$$ find $I(14,28)$

elfin berryBOT
rich isle
#

HERE

stoic saddle
#

aight wait

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you give two different defns for I(n,a)

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one of which is a function of x and another which isnt

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inconsistent much?

rich isle
#

the second one was given

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i derived the 1st one

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easy

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???

stoic saddle
rich isle
#

i first did it for my actual expression, for 1-2x whole to the power 28, hence got 54 in that 2nd term involving i(n)

rich isle
# elfin berry **.**

but otherwise, generally, the 1st expression is the recurrence relation needed here

marsh citrusBOT
#

@rich isle Has your question been resolved?

marsh citrusBOT
#

@rich isle Has your question been resolved?

marsh citrusBOT
#

@rich isle Has your question been resolved?

rich isle
#

<@&286206848099549185>

#

@stoic saddle

earnest canopy
#

Can you send the question again?

rich isle
past thicket
twin pike
#

like

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taking x-x^2 as some variable z

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the expression becomes [(z)(1-4z)]^14

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smthing like that mybe

rich isle
#

no

rich isle
#

<@&286206848099549185>

rich isle
#

the present one is messy

brave knoll
#

Notice that d(x-x²) = (1-2x)dx and that here 2n = a

rich isle
#

<@&286206848099549185>

brave knoll
#

You may find errors but it really is the idea

rich isle
#

illse sire

#

well i am a pre-uni fella so maybe i cant understand all of it but still

brave knoll
#

there is a small sign error in the IBP but the computation remains coherent

rich isle
rich isle
#

<@&286206848099549185>

hollow urchin
#

I would write $(x-x^{2})^{n}$ as $x^{n}(1-x)^{n}$ and then do ibp

elfin berryBOT
#

డ్ర్యాగ్లొక్స్

solar elbow
#

can anyone solve these

cunning fiber
marsh citrusBOT
brave knoll
#

A way to solve I(14,28) is to expand the terms raised to the power 14 / 28
It demands a lot of computation (using Newton Binomial formula) but it gives the solution

stone shale
#

help please

worldly crag
#

and id say also write out the formulas for area and pythagorean theorem on an equation

heady forge
#

<@&268886789983436800>

stone shale
#

PELASE HELP!!EEEE

simple crane
#

the question stated what to do.

marsh citrusBOT
#

@rich isle Has your question been resolved?

cunning fiber
marsh citrusBOT
marsh citrusBOT
#
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true notch
#

i give up on this can someone pls explain the entire thing like how did your brain work through finding patterns to figure this out

true notch
#

like i was thinking after the 3rd term, we can see that it becomes 2^1, then 2^2, then 2^3

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and we also notice that the difference between the terms after the 2nd and 3rd also go up by 2^1, 2^2

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for example, 5-3=2, 9-5=4, 17-9=8 and so on

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so what i came down to was (2^(n-4)) / (2^(n-2)) but obviously this doesnt work for the 2nd term

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then i looked at them seperately and still couldnt figure it out

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so i give up and require help

iron marlin
#

Yeah you already guessed a formula right, try getting it right for everything from the 2nd term onwards

fringe nacelle
#

just use OEIS

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on the numerators and denominators

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<@&268886789983436800>

true notch
iron marlin
#

Though you could argue the formula is
n=1...6: these 6 terms
n=7...: always 19

fringe nacelle
#

the answer is not unique, so, any answer will do

#

this isnt a math problem

true notch
fringe nacelle
iron marlin
fringe nacelle
#

1/4, 1/3, 2/5, 4/9, 8/17, 16/33, 19, 19, 19, 19, 19, 19, 19, ..., 19, ...

slim shard
iron marlin
#

which is a valid continuation of a sequence, just probably not what the person who set the question had in mind

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unless that person is me

iron marlin
#

the first term might be a bit problematic for now

true notch
iron marlin
true notch
#

idk

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i mean i couldnt figure out a way to modify it so that it would fit

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the entire series

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it always breaks on the second term

iron marlin
#

Fit second term onwards first

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Ignore the first term for a bit

true notch
#

ok

#

let me try with that in mind

wary kite
#

consider multiplying each of the fractions for n >= 2 by 2/2

#

pattern should be clear

#

$\frac{1}{4}, \frac{2}{6}, \frac{4}{10}, \frac{8}{18}, \frac{16}{34}, \frac{32}{66}, \dots$

elfin berryBOT
haughty zephyr
true notch
#

so it just comes down to figuring out if its possible to unsimplify the numbers

#

then going for patterns from there?

wary kite
haughty zephyr
true notch
#

.close

marsh citrusBOT
#
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opaque sleet
marsh citrusBOT
opaque sleet
#

im so stuck after this part

wary kite
#

what about it?

#

split the fraction

#

do you know how to integrate 1/2 and 1/2 cos(2x)?

opaque sleet
#

so

#

its

1/2 times 1/2 and then + 1/2 times cos2(theta)

winged delta
#

yes

wary kite
#

no

opaque sleet
#

what

#

i got the 1/2 from the 1+ cos2theta / 2

winged delta
#

$\int (f + g) = \int f + \int g$

elfin berryBOT
#

Médicis

wary kite
#

yea but you have an additional 1/2 on the 1/2 which presumably comes from the factor outside the integral

#

if you want to distribute it inside the integral then it also needs to be multiplied by the 1/2 cos(2x)

opaque sleet
#

lets do it step by step my brain is not getting it

wary kite
#

$\frac{1}{2} \int \frac{1}{2} + \frac{1}{2} \cos 2\theta \dd{\theta} = \int \frac{1}{4} + \frac{1}{4} \cos 2\theta \dd{\theta}$

elfin berryBOT
wary kite
opaque sleet
#

so u got that first 1/2 because it was already from 1/2 cos^2 theta d theta

#

then after the integral

#

the 1/2 is the 1+ cos2theta / 2

wary kite
#

what is unclear?

opaque sleet
#

the 1/2s

wary kite
#

what about them

opaque sleet
#

i understand the 1/2 before the integral

wary kite
#

that comes from splitting the fraction

#

$\frac{1 + \cos 2\theta}{2} = \frac{1}{2} + \frac{\cos 2\theta}{2}$

elfin berryBOT
opaque sleet
#

okay i understand

#

the splitting fraction part

#

now we integrate

wary kite
#

yes

opaque sleet
#

so i want the first 1/2 to go out

#

making the 1/2 outside 1/4

wary kite
#

sure

opaque sleet
#

but theres an extra theta idk where that came from

wary kite
#

$\frac{1}{4} \int 1 + \cos 2\theta \dd{\theta}$

elfin berryBOT
opaque sleet
#

wait whered u get the 1

wary kite
#

🤔

#

didn't you just say you wanted to pull the 1/2 out

#

as a factor

opaque sleet
#

well yeah

#

wouldnt it be

1/ 2 times 1/2

wary kite
#

$\frac{1}{2} \int \frac{1}{2} + \frac{1}{2} \cos 2 \theta \dd{\theta} = \frac{1}{2} \int \frac{1}{2}(1 + \cos 2\theta}) \dd{\theta}$

elfin berryBOT
#

knief
Compile Error! Click the errors reaction for more information.
(You may edit your message to recompile.)

wary kite
opaque sleet
opaque sleet
wary kite
opaque sleet
#

okay i see now u bascially factored out the 1/2?

#

so now

#

u kick out that 1/2

#

and then whats left inside is the

1 + cos2theta

#

now we integrate

#

step by step

#

1 is just theta

#

and multiply by 1/4 so thats how u got 1/4 theta

#

so now we have cos2theta

#

which is sin^2 / 2 times 1/4

wary kite
#

what

opaque sleet
#

wops

#

i forgot what the integral cos^2 theta is

wary kite
#

its not cos^2

#

its cos(2theta)

opaque sleet
#

oh crap right

#

so i kick out the 2 there from cos2theta

#

that makes my 1/4 into a 1/8

#

i have it written down as

1/4 times cos2theta

#

i get it wrong sometimes and do 2/8 instead of 1/8

#

how do i avoid that

wary kite
#

take the factor of 1/4 then divide by 2 for reverse chain rule on cos(2theta)

#

cos turns into sin

#

because sin differentiates to cos

opaque sleet
#

oh timeout

#

this part

#

didnt we kick out 2 on the sin

#

to make our 1/4 to 1/8

wary kite
opaque sleet
#

would this be written as

1/ 4 times sin 2theta / 2 + c

wary kite
#

why not make it 1/8

opaque sleet
#

yeah but before it becomes a 1/8

#

i mean

opaque sleet
wary kite
opaque sleet
#

so

#

this part here

wary kite
#

what about it

opaque sleet
#

i mean this whole part here

we got the one on the left side fine

wary kite
#

sin(2x) = 2sinxcosx

opaque sleet
wary kite
#

double angle identity

opaque sleet
#

ok great

#

this part is the part where u go back to x is what i understand

#

i think i got it from here

#

thank you

#

.close

marsh citrusBOT
#
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marsh citrusBOT
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umbral moon
#

help?

marsh citrusBOT
umbral moon
#

its not 92.9697

#

or 93.0093

fervent rampart
#

caan you show how you got your answer?

umbral moon
nimble prairie
#

or, what do u need help with?

wary kite
nimble prairie
#

Notice that u have a geometric series

umbral moon
nimble prairie
#

Do u know how to compute a convergent geometric series?

umbral moon
#

i don't have my notes with me i forgot at friends house so it's hard to do the hw rn, like for me to do, ykwim

wary kite
#

you'll find some videos

umbral moon
#

!close

#

.close

marsh citrusBOT
#
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lusty island
marsh citrusBOT
lusty island
#

i did some rough work

#

just to visualize

#

the question a little bit

#

but dont know how to even begin proving here

ruby mulch
#

Tips: there should be a neat bijection by marking "1" as the "start of the number"

marsh citrusBOT
#

@lusty island Has your question been resolved?

lusty island
#

is this for if the compisition starts with 1 or 2?

ruby mulch
#

You first prepend the composition with "1"

lusty island
#

ok...

ruby mulch
#

Note that:

1 = 1
3 = 1 + 2
5 = 1 + 2 + 2
7 = 1 + 2 + 2 + 2
...
lusty island
#

right

lusty island
ruby mulch
#

For example, for n = 5, the possible compositions are:
5, 3 + 1 + 1, 1 + 3 + 1, 1 + 1 + 3, 1 + 1 + 1 + 1 + 1 = 5
Rewrite it in the above rule results in:
1 + 2 + 2, 1 + 2 + 1 + 1, 1 + 1 + 2 + 1, 1 + 1 + 1 + 2, 1 + 1 + 1 + 1 + 1 = 5
Now, if you drop the leading one, you get:
2 + 2, 2 + 1 + 1, 1 + 2 + 1, 1 + 1 + 2, 1 + 1 + 1 + 1 = 4

#

Sounds familiar?

lusty island
ruby mulch
#

Yes

lusty island
#

i think i get it

#

let me write some stuff and send a solution

lusty island
#

@ruby mulch

#

ignore the visuals

#

thats for me

#

to understand lol

#

thanks for the help

#

i dont know how you guys come up with proofs so well

#

.close

marsh citrusBOT
#
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marsh citrusBOT
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clear crane
#

i ran through this problem and dont know what to do

clear crane
#

Find the absolute extrema of the function on the closed interval.

agile karma
#

What have you tried?

clear crane
#

i tried solve for the derivate of that problem

#

set it = to 0

#

and put x = -3 , x = 6 for the derivate

agile karma
#

Did u try using the x value from when u set the derivative to 0?

clear crane
#

this is my work

gusty flame
clear crane
#

oh i forgot x= 1

#

yea my bad

#

js saw that too

agile karma
#

your maximum looks right

gusty flame
#

Happens

agile karma
#

well- the x value is right

#

make sure u remember to plug your x value into the original function, not the derivative

clear crane
#

oh

agile karma
#

Do u know why?

#

and your minimum x value is wrong

clear crane
#

i try to put it to canvas

#

idk what graph to look for

agile karma
#

Do u know what the derivative means in context of the original function?

clear crane
#

hmm just one degree less?

agile karma
#

Not quite

clear crane
#

i actually dont know what is the derivate, i just apply the formula lol

agile karma
#

Okay

clear crane
#

or sometime they ask to find a slope

agile karma
clear crane
#

i do the derivate, put given x into the derivate to find slope

#

and do y-y1 = m(x-x1)

agile karma
#

Okay

#

so, if, for example

#

i have a function f

#

and i evaluate the derivative of that function at, say, x=3

#

i get..?

clear crane
#

f'(3)

#

you get slope??

agile karma
#

exactly

#

you get the slope of the curve at that point

#

give me one second...

clear crane
#

okk....

agile karma
#

say the blue graph is my function

#

and the red line is a tangent to the function at x=3

#

then the derivative of f at 3, f'(3), will give me the gradient of that tangent

#

So what do you think happens when I take the derivative of a function, and set it equal to 0?

clear crane
#

you will get the minimum

#

or it will give you a x value

agile karma
#

It will give me an x value, yes

#

but what does that tell me about the original function at those points?

clear crane
#

oh ...... a tangent line pass through the point

agile karma
#

Not quite

#

The derivative always tells me the gradient of the tangent for a graph

#

so if my derivative is 0, then the gradient of my tangent is..?

clear crane
#

would probably to 0 as well

#

or would it be constant

agile karma
#

it would be 0, yes

#

which would mean it's a straight line

#

so if we look at this function, the derivative should be equal to 0 where?

#

try imagine the tangent at different points

clear crane
#

i think that is where slope = 0

agile karma
#

exactly

clear crane
#

its a constant line

agile karma
#

exactly

#

so, for any function f, setting the derivative to 0 and solving for x will give me the x-values for..?

clear crane
#

oh

#

minimum and maximum

agile karma
#

yes, (and stationary points of inflection, but we dont need to worry about that here)

#

So if we go back to your original function

clear crane
#

wait....

#

is this correct

agile karma
#

$f(x) = x^3 - \frac{3}{2} x^2$

elfin berryBOT
agile karma
#

are you sure that's the absolute maximum though?

clear crane
#

yea i would say unsure as well

#

because the graph goes infinity

#

i think that is relatve max

agile karma
#

yes

clear crane
#

i was gonna ask you about that question but idk how to say

agile karma
#

let's pretend that's the whole graph

clear crane
#

so abs max = DNE

agile karma
#

so if we go back to your original function- how would you approach finding the absolute minimum and maximum?

#

(remember the closed interval)

clear crane
#

i just plugged in x to the original function

#

because that is where the line touch the lowest close interval

#

and would do the same thing to find max

#

hmm for this problem is it true that i wasted time doing the derivate, i just plugged in x = - 3, x=6 i have my min and max already

agile karma
#

For this specific one- yes

#

But that might not hold true for every function

clear crane
#

yea

#

usually odd function right

agile karma
#

it's useful to know how to find minimums and maximums with the derivative

clear crane
#

ok i have a similar problem

#

let me try to do it

agile karma
#

Go for it

clear crane
#

the problem with this is that , i got the minimum wrong

#

i try to set the problem = 0

#

hmm i think i forgot the set the orinigal equation x = 0

agile karma
#

Nah, you wouldnt set the original equation to 0

#

There's an error in your working when u set the derivative to 0

#

2/(3sqrt(x)) cubed isn't x/8 * 8/x

#

instead of cubing, try squaring

clear crane
#

like ()^2 ?

agile karma
#

yes

clear crane
#

....

#

ok here

#

oh oh then i just multiple both side with denominator

#

i found x =0

#

now plug it in to find the minimum value

agile karma
#

waitt my bad i misread your original working

#

Nevermind- u were right the first time

#

that's my mistake

#

The derivative is 0 when x=1, yes

clear crane
#

oh ok

agile karma
#

But it's not quite the minimum still

clear crane
#

but that isnt the answer for the minimum

agile karma
#

yes, it's not

#

there's one more point u might want to check

#

u were close

clear crane
#

is it factor??

agile karma
#

nah not quite

#

think about it graphically

#

what does the graph of $3x^{2/3} -2x$ look like

#

doesnt need to be technical, just a rough drawing is fine

elfin berryBOT
clear crane
#

hmm

#

no idea

#

but i can use desmo

#

i mean

#

using desmo

#

it gave the sauce already

#

my bad on this one i do not what the graph looks like without desmo

#

it would take me years

agile karma
#

lol

clear crane
#

actually not years, i just plug in x = 0,1,2,3

agile karma
#

if u ever want to graph it without desmos

#

think of the graph as two different functions

#

3x^(2/3)

#

and -2x

#

and you're just adding them together

#

you can graph both of those by themselves, then draw your function

clear crane
#

yea

agile karma
#

So what have you got for your minimum?

clear crane
#

i put 0 in for x

#

lowkey it tells me that 3(0)^2/3 - 2 ( 0 ) would just be 0

#

anything time 0 = 0

#

i got (0,0) for minimum

agile karma
#

That sounds right

clear crane
#

yea thanks to desmo for that

#

but it lowkey works for me

#

thanks for the help !! really appriciate it

agile karma
#

no worries

#

good luck

marsh citrusBOT
#
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marsh citrusBOT
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hexed sigil
#

in linear algebra, if i know the standard matrix representation of two linear transformations $K, S$, is the standard matrix representation of $K + S = [K] + [S]$?

elfin berryBOT
#

dis_da_mør

crisp lagoon
#

I ended up getting the correct answer but I am not convinced with the method I used to solve I am sure there are plenty of mistakes
Someone pls tell me how can I better approach questions like these

hexed sigil
#

sorry this channel is occupied

crisp lagoon
#

Ohh my bad

#

Are there any free ones?

hexed sigil
#

yep check the above category, like #help-45

crisp lagoon
#

Thanks

hexed sigil
#

re-sending the original question:

#

in linear algebra, if i know the standard matrix representation of two linear transformations $K, S$, is the standard matrix representation of $K + S = [K] + [S]$?

elfin berryBOT
#

dis_da_mør

hexed sigil
#

from what i can see if both transformations have the same origin and destination vector spaces (so their matrices are the same size) then yes

#

.close

marsh citrusBOT
#
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halcyon elk
#

"the ratio between the reading of the ameter before and after closing K"

halcyon elk
#

how is it any of these options...?

#

before closing k, the whole current would go thru the ameter

#

so it would be I""

#

after closing K, the current is gonna be split in half

#

so... 1/2 I

#

I / (1/2 I) is 2

#

which is not in the options

fervent rampart
#

but the current is also higher after closing the switch because the whole circuit has less resistance

halcyon elk
#

1 / (2/3)...?

#

I calculated the overall R, did Vb/R, split that into two

#

I : 2/3 I

#

yeah its right

#

ty cloud

#

.close

marsh citrusBOT
#
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clear arrow
#

Hello! I am working on a proof of this exercise from Herstein's "Topics in Algebra":

clear arrow
#

Sketch of my proof goes as follows. The first sentence in the problem is basically a fancy way of saying that left coset equals right coset for all elements of G, i.e. Ha = aH.

#

And if so, we can easily prove that gHg^{-1} = H for all g from G. (because gH = Hg means that for every h from H, there is a h' from H such that gh = h'g, then we can multiply by g^{-1} on the right and get ghg^{-1} = h' which would eventually establish that gHg^{-1} = H for all g. So as a side effect we will establish what is asked in the exercise (i.e. that gHg^{-1} is a subset of H).

elfin cairn
#

Yes

clear arrow
#

my question is: why does Herstein ask for something milder?

#

i.e. why doesn't he ask to prove a stronger result (equality of sets rather than just A is subset of B)?

#

am I missing something in the statement?

elfin cairn
#

First, these are equivalent

#

This inclusion implies equality

clear arrow
#

because there is a bijection between the two?

#

so they have equal number of elements, hence there can't be anything missing on the left?

elfin cairn
#

In the finite case that will work

clear arrow
#

well, in the finite case, yes

elfin cairn
#

But generally the double cosets form a partition of your group

#

And so if any two (double) cosets have a non-empty intersection then they are equal

clear arrow
#

I haven't got to double cosets yet 🙂

#

is that like aHa{-1} ?

elfin cairn
#

Really it just aHb instead of aH or Ha

clear arrow
#

ok

#

OK, I see, so basically we are saying that H is a double coset (with a=e, b=e) and gHg^{-1} is a double coset (with a=g, b=g^{-1}), and they have non-empty intersection (because one is included in the other and is not empty), and since they form a partition (just like normal cosets) - they are equal

elfin cairn
#

Yes

clear arrow
#

OK, so the summary is that Herstein is asking us to prove something equivalent (that looked weaker to me, because I didn't know that it was equivalent -- or at least I have to prove that). I suspect though that he may have had some other proof in mind, that would more naturally lead to that subset formulation...

#

but there is no way to tell because there are no official solutions from Herstein himself 🙂

elfin cairn
#

Ptobably something like, take x=ghg^-1

#

And take a look at the coset Hx

#

Showing it must be equal to H somehow

clear arrow
#

but then elements of that coset would be hghg^-1?

#

i.e. with two "h"s

#

I found this exercise quite confusing overall, especially before I reformulated the first assumption to simple aH=Ha. Actually I came to this from the end, i.e. I've just seen this property of cosets (that aHa^-1 = H if aH=Ha) in another book and then I realised that I just need to show that aH=Ha and then I am done. And then I realised that the assumption of the problem is just equivalent to that -- it took some time to persuade myself 🙂

elfin cairn
#

Maybe its a good idea to gather your reasoning on why is this statement is equivalent

clear arrow
#

on equivalence of "aH=Ha" and "whenever Ha != Hb then aH != bH"?

elfin cairn
#

Yes

marsh citrusBOT
#

@clear arrow Has your question been resolved?

clear arrow
#

my reasoning went like this. Let's reverse Herstein's statement (i.e. make a contrapositive statement). Then it becomes "if aH=bH then Ha=Hb" (for all a,b from G). In words, alternatively, "if two elements are in the same left coset, then they are in the same right coset". We know (from previous exercises or the book) that left cosets (and right cosets too) form a partition of G. A partition of a set is fully defined by specifying for each pair of elements whether they are in the same part or not (because this relation "a and b are in the same part" is basically the same relation for corresponding equivalence relation). And our statement said that "if two elements are in the same left part, then they are in the same right part", so this relation is defined identically on one partition and and on another, leading to the same parititions for all a and hence aH=Ha in general. But this one is somewhat messy (and also it looks like our statement about pairs goes only in one direction A -> B, not necessarily A=B, so I need to do some workaround for that too)

#

there is probably a simpler way of demonstrating this...

elfin cairn
#

Using this observation and using a two sided inclusion to prove aH=Ha can work

#

If you want to go through the details

#

if x in aH then xH=aH and and so Ha=Hx, and so x = e * a in Ha

#

The one sidedness of the given statement is not a problem as if aH=bH then
Ha^-1=Hb^-1 by taking the inverse

clear arrow
#

yeah, makes sense

elfin cairn
#

Oh I see you are a factorio gamer xD

#

Love this game

clear arrow
#

haha, yes, it's good, but I only played a little, should come back to it at some point, it was fun

elfin cairn
#

I have 1300h on it 😵‍💫

#

And I am always just messing around

#

Late game of the new dlc is tough

clear arrow
#

wow 🙂 that's definitely not "a little"! 🙂

#

for me it was like this: I liked the game and started to "sell" it to my friend, who got hooked, and then somehow I myself almost stopped playing it 😅

elfin cairn
#

The ability so sit down an truly enjoy gaming has been going up and and down in phases

#

Right now I found two new games to add to my top 10 ever.

clear arrow
#

what are they?

elfin cairn
#

Finished one already, and having fun with the other

elfin cairn
clear arrow
#

ah yes, got those two on Game Pass, but haven't played yet, only watched some let's plays on YouTube 🙂

#

I recently played Baldur's Gate 3 and Kenshi 🙂

elfin cairn
#

When the time comes I might play one of them

#

I have enough things related and not related to gaming to do

clear arrow
#

yeah, so many games to play!

#

so many areas of math to study 😄

elfin cairn
#

you have rings, fields and then dozens of ways to continue

#

I am currently battling Algebraic Geometry

clear arrow
#

I also wanted to discuss my study plan, but that's probably something that's better to do in the relevant channel for abstract algebra

elfin cairn
clear arrow
#

and another time, because I need to get back to work 🙂

elfin cairn
#

Cya

clear arrow
#

thanks for your help, see you!

#

.close

marsh citrusBOT
#
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marsh citrusBOT
#
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stone hound
#

lim f(phi) = f( lim phi )

marsh citrusBOT
indigo nest
#

!original please

marsh citrusBOT
#

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

stone hound
#

Help me with the last property

indigo nest
#

Ah limits commute with continuous functions

stone hound
#

Wait

#

Can you elaborate?

#

Please look at this

#

I somehow did it

marsh citrusBOT
#

@stone hound Has your question been resolved?

stone hound
#

<@&286206848099549185>

marsh citrusBOT
#

@stone hound Has your question been resolved?

stone hound
#

.close

marsh citrusBOT
#
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#
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leaden peak
marsh citrusBOT
leaden peak
#

Official explanation

#

my answer: 16 sqrt 2

#

my reasoning: side is 32, center of the circle would be center of the square, so find half diagonal length

#

$\frac{\sqrt{32^2 + 32^2}}{2}=16\sqrt{2}$

elfin berryBOT
#

UCYT5040

stoic saddle
#

that is the distance from A to the center

#

and not to the circle itself

leaden peak
#

so it means like, to the nearest point on the circle?

ionic ferry
#

Ahhh yeah, they're not asking to centre of circle, only the circle

leaden peak
#

oh so then since the radius is 16

#

just subtract that from half diag

ionic ferry
#

Yup

leaden peak
#

ok that makes sense

#

just kinda confusing cause i always saw circle notation as like O(x, y)

#

but i guess it makes sense its not talking about the center, thats just a way to identify the circle

ionic ferry
#

That's fine dude even I was confused there for some time

leaden peak
#

ok thank you so much, guess this problem wasnt that hard lol

#

.close

marsh citrusBOT
#
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fervent burrow
#

hi, can anyone help me understand this concept? its factoring quadratics, ive tried different explanations but none of them really make sense to me.

fervent burrow
#

i promise im in college 😓 i just have difficulty understanding formulas

past thicket
#

,rccw

elfin berryBOT
brave knoll
#

for this particular case I would just have computed the roots

#

otherwise it's about guessing and training

slim shard
#

lol with such an unclear explanantion i dont blame you for not understanding

fervent burrow
#

yes exactly lol

#

im mostly confused on how to get the last two terms on the last step

#

i dont really understand where the 2 and -8 came from other than the -16, and if thats the case whats the point in multiplying the first and third number 😓

obtuse umbra
#

do you know about the complete the square method?

#

i think this one is easier for you to follow

fervent burrow
#

would that work if its not an equation?

obtuse umbra
#

it works for most of the quadratics

#

so take the quadratic $9y^2 - 18y - 16$ as what it said

elfin berryBOT
#

1 divided by 0 equals Infinity

obtuse umbra
#

do you notice that $(3y)^2 = 9y^2$?

elfin berryBOT
#

1 divided by 0 equals Infinity

fervent burrow
#

writing down rn

#

yes

obtuse umbra
#

the purpose of this method, is to make a square

#

and what is $(a + b)^2$ and $(a - b)^2$?

elfin berryBOT
#

1 divided by 0 equals Infinity

obtuse umbra
#

if you can't remember the formula, then just distribute it all out

fervent burrow
#

wdym?

obtuse umbra
#

what i mean is that

obtuse umbra
elfin berryBOT
#

1 divided by 0 equals Infinity

obtuse umbra
#

and $(a - b)^2 = a^2 - 2ab + b^2$

elfin berryBOT
#

1 divided by 0 equals Infinity

obtuse umbra
elfin berryBOT
#

1 divided by 0 equals Infinity

fervent burrow
obtuse umbra
#

wait

#

3y acts as a

#

and we want 18y to act as 2ab

#

notice that 18y = 2 . 3y . 3

#

so b can act as 3

#

since we only need b^2 left, we can seperate -16 into 9 - 25

#

so it should be something like

#

$(3y)^2 - 2 \cdot 3y \cdot 3 + 9 - 25$

elfin berryBOT
#

1 divided by 0 equals Infinity

obtuse umbra
#

turns into $(3y - 3)^2 - 25$

elfin berryBOT
#

1 divided by 0 equals Infinity

obtuse umbra
#

do you get what i mean now?

fervent burrow
#

not really

#

its not the correct answer and im guessing thats why i have to use that formula

obtuse umbra
#

that's not the answer yet

#

now do you know the difference of squares?

fervent burrow
#

im just more confused now

#

idk

obtuse umbra
#

if you are confused about the formulas

#

try to discover why they are true

#

for example: $(a + b)^2 = a^2 + 2ab + b^2$, why?
because $(a + b)^2 = (a + b)(a + b) = a^2 + ab + ab + b^2 = a^2 + 2ab + b^2$

elfin berryBOT
#

1 divided by 0 equals Infinity

obtuse umbra
#

the same reason applies for $(a - b)^2 = a^2 - 2ab + b^2$

elfin berryBOT
#

1 divided by 0 equals Infinity

obtuse umbra
#

that is one way to remove your confusion of the formulas

#

they exist because they have proven it

marsh citrusBOT
#

@fervent burrow Has your question been resolved?

#
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marsh citrusBOT
#
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marsh citrusBOT
past thicket
#

Huh?

#

<@&268886789983436800>

ionic ferry
#

ummmm

quiet anvil
#

no

past thicket
#

Also using an llm to scam is pathetic lmfao

marsh citrusBOT
#
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oak oxide
#

gasp huh

main idol
past thicket
oak oxide
#

What's Q4

#

Ehhh I can't understand

past thicket
quiet anvil
#

quarter 4

#

it's financial bullshit

marsh citrusBOT
#
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vital yew
#

Find the number of ways in which two small squares can be selected on the normal chessboard if they are not in same row or same column.

vital yew
#

My answer is 64*49 , but idk the answer is given 32X49

vagrant raft
#

You overcounted each position twice

vital yew
#

Yes , that's written int he solution......

#

But why

#

I mean normall

#

y

#

when I use principle of counting I don't think of overlapping

#

Why for this specific case I have to

vagrant raft
#

Think about how you picked your squares

vital yew
#

Yes....... i had 64 choices for the 1st square and for each correspond square I had 49 choices