#help-49

1 messages · Page 263 of 1

vague seal
#

yes

sullen bolt
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pls wait til i get the integral

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(3 mins)

last slate
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Factorize the terms.

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(x-1)(x-2)(x-3)

last slate
#

And now use partial fractions.

sullen bolt
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I know lmao

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just figuring out the top part of the partial fractions

last slate
sullen bolt
#

should I just matrix this lol

red cloak
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4th one

sullen bolt
#

!occupied

last slate
midnight plankBOT
#

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

red cloak
red cloak
orchid fossil
sullen bolt
#

is the result perhaps
$\frac{\ln(x-1)}{2}-\ln(x-2)+\frac{ln(x-3)}{2}$

last slate
grand pondBOT
#

laestia

sullen bolt
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unless I'm dumb

sullen bolt
#

the pfd results is 1/2(x-1)-1/(x-2)+1/2(x-3)

last slate
#

OH WAIT.

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No.

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On the denominator.

last slate
sullen bolt
#

so ts is correct right

last slate
red cloak
#

It's this one is basic qn of integration

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Just some simplification

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And it's done

last slate
red cloak
#

Can you solve mine @sullen bolt

sullen bolt
midnight plankBOT
sullen bolt
#

if you want help, open a new help channel

hexed barn
red cloak
sullen bolt
#

.solved

midnight plankBOT
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last slate
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tame osprey
#

is there any other way to do this without assuming ϴ = 90°

last slate
fathom onyx
#

Note that cosec = 1/sin, solve the quadratic in sine-theta, and evaluate the desired value

fathom onyx
civic gazelle
fathom onyx
#

that too

tame osprey
#

.solved

midnight plankBOT
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silk forge
civic gazelle
#

x = -1:

silk forge
#

yes for positive numbers

civic gazelle
#

is sin x always positive then

silk forge
#

for negative it is -2 to - inf

last slate
#

When sin is +ve, cosin is +ve.

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So you can kinda use it.

silk forge
#

its obv

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that u wont get 2

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if sin takes a negative value

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so i didnt bother

last slate
#

hi

last slate
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last slate
#

oh nvm

midnight plankBOT
last slate
#

...

graceful drum
#

you can close the channel with .close

frigid gorge
#

lol

last slate
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.close

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meager cypress
#

Whatt

midnight plankBOT
meager cypress
#

Close

rich yew
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.close

fathom onyx
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.close

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shut canyon
midnight plankBOT
shut canyon
#

a guess is that maybe if the two curves intersect f(x)=x at the same two points something is …

midnight plankBOT
#

@shut canyon Has your question been resolved?

midnight plankBOT
#

@shut canyon Has your question been resolved?

shut canyon
#

h(x) = α₁ x + 1/2.

#

h ∘ Qc = Fμ ∘ h

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.close

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leaden seal
#

someone help me differentiate this i keep getting it wrong

mystic condor
#

what are the symbols?

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is it theta and phi?

leaden seal
#

yes

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and theres also alpha

leaden seal
fathom onyx
#

And you aim to differentiate with respect to...?

leaden seal
fathom onyx
#

What have you tried, if anything?

leaden seal
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and thats about all

sharp coral
#

@vast citrus this channel is for helping zah with her geometry homework. please keep it on topic

fathom onyx
#

Wrong place, and I could swear this has been done multiple times.

fathom onyx
#

Wait hold on, not even that

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You're differentiating with respect to PHI, right?

leaden seal
#

yeah and so the other terms are constant

fathom onyx
#

Then the whole part before the cosine-reciprocal thing, relative to PHI, is just a constant, yh

leaden seal
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right?

#

thanks

fathom onyx
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Because nothing there depends on phi

merry shale
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😒

fathom onyx
#

And where here does the tangent function even appear?

merry shale
#

cant you combine sin and cos

fathom onyx
#

No?

merry shale
#

cus cos is to the power of negative one

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so it becomes denominator

fathom onyx
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That'd only apply if the arguments of both the sine and cosine matched

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But they DON'T match

merry shale
#

oh damn i didnt read

#

mb

fathom onyx
fathom onyx
# leaden seal

I don't quite agree that this is the derivative of that section btw

leaden seal
#

oh

fathom onyx
#

The Chain Rule applies here too, so you have to multiply this result by the derivative of cos(phi - theta) [with respect to phi]

leaden seal
#

yeah

fathom onyx
#

So the outer function (the -1 power), that derivative was fine

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The inner function is cos(phi -theta)

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What's the deriv. of cosine?

leaden seal
#

-sine

fathom onyx
#

ye

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So what's the d/dphi of cosine(phi - theta)?

leaden seal
fathom onyx
leaden seal
#

so -sin(phi - theta)

fathom onyx
#

yee

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Now multiply that with that ^-2 thing and the coefficient of that original cosine (that is, the w sin() thing)

midnight plankBOT
#

@leaden seal Has your question been resolved?

leaden seal
#

so we use power rule for this part

#

.close

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tidal turret
midnight plankBOT
tidal turret
midnight plankBOT
#

@tidal turret Has your question been resolved?

tidal turret
#

i think i can simplify a bit more the second system

midnight plankBOT
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@tidal turret Has your question been resolved?

midnight plankBOT
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@tidal turret Has your question been resolved?

midnight plankBOT
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@tidal turret Has your question been resolved?

signal ibex
#

i am not sure how much mileage ill get with the explanation but seeing the problem being up this long, can't hurt to try

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start by finding all candidate optimizers (gradient = 0, which translates into 3x^2 - 2y = 0)

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then check each boundary seperately

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the harder one is $1/2 x^2 + 1/4 y^2 = 1$

grand pondBOT
#

king of complex analysis

signal ibex
#

thats what i get for not using \frac

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anyway

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isolate for y^2

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$y^2 = 4(1 - \frac{1}{2}x^2$

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$y^2 = 4(1 - \frac{1}{2}x^2)$

grand pondBOT
#

king of complex analysis

signal ibex
#

doing it this way, easier algebra

#

sub that in and find extrema along that boundary by taking the derivative with respect to x (you eliminated y)

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then repeat with the other boundary

tidal turret
#

\textbf{2.} Find, if they exist, the absolute extrema of
[
f(x,y) = x^{3} - y^{2}
]
restricted to the region
[
A = {(x,y)\in \mathbb{R}^{2} : \tfrac{1}{2}x^{2} + \tfrac{1}{4}y^{2} \le 1,; y \ge \sqrt{2},x }.
]

grand pondBOT
#

Renato

tidal turret
worthy hill
#

draw.

frank wolf
tidal turret
#

hey

frank wolf
#

Still having trouble with the problem?

tidal turret
#

yes

queen herald
# tidal turret

Okay, you got x^2=1. Hence x = 1 or -1, right? Then you can sub x into the first 2 equations and solve for lambda1 and lambda2

#

You learnt how to solve systems of equations, right?

midnight plankBOT
#

@tidal turret Has your question been resolved?

gilded viper
#

@tidal turret é brasilieiro?

signal ibex
#

like, the thing to find the extrema of

signal ibex
#

easier to do it this way because there is no square root business, isolating x is harder

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full grail
#

hi can someone help idk how to integrate this

midnight plankBOT
radiant roost
#

if you do integration by parts, can you get the sqrt into the denominator?

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oh i thought that would make it look like the derivative of arcsin, but the sign is wrong

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i think your simplification went wrong somewhere along the way

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yeah i think the u-sub is not working

native swift
#

may put u = cos t
with Bioche rules

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not -cos t

wet pollen
#

Eliminate the root with another substitution.

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5u^2 = 9tan^2(v)

radiant roost
#

you didn't change the limits when you did the u-sub

full grail
#

yea I was fonna change everything back

#

Look

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Bruh this is disguting

radiant roost
#

i think you can substitute u = t - pi

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on the fifth line

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then you get an odd function

raven oak
#

cant u rearrange cos double angle identity to replace cos^2

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nvm i am blind

wet pollen
#

What's the original question?

radiant roost
#

,align S&=4\pi\int_0^{2\pi}\sin(t)\sqrt{9-5\cos^2(t)}dt\
&=4\pi\int_{-\pi}^{\pi}\sin(u+\pi)\sqrt{9-5\cos^2(u+\pi)}du\
&=-4\pi\int_{-\pi}^{\pi}\sin(u)\sqrt{9-5\cos^2(u)}du\
&= 0

grand pondBOT
midnight plankBOT
#

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mint ravine
#

please help

midnight plankBOT
mint ravine
#

is there a smarter way than just doing casework for billy's position

#

@help

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helper

radiant roost
#

I think you can make an argument for 1/3 based on symmetry

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Like you can partition the space of orders based on the equivalence relation that permutes the triplets

mint ravine
radiant roost
#

Ex one part in the partition might be
138AB276C45
138AC276B45
138BA276C45
138BC276A45
138CA276B45
138CB276A45

#

The probability here is 2/6, and the same goes for every other part

mint ravine
#

oh ok that makes sense

#

thanks

#

.solvee

#

.close

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stable halo
midnight plankBOT
stable halo
#

yea cane someone do this for me i aint tryna do all that

midnight plankBOT
stable halo
#

i just think its stupid to set such a qwuestionb

#

.close

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fallow scarab
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uncut maple
#

$\int \frac{1}{1+\cos{x}}$

midnight plankBOT
grand pondBOT
#

felipe

uncut maple
#

I know u can substitute t = tan(x/2) or multiply the equation by 1-cosx/1-cosx

#

My question isn't solving, but why can you multiply it by 1-cosx/1-cosx? How can you guarantee that cosx isnt 1? In that case you would be multiplying by 0/0

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prob a stupid question but i have to ask it lol

polar mortar
#

when you do this you generally (implicitly) assume you're excluding values where you divide by 0

uncut maple
#

oh, I thought about that but wondered if there was something else

#

Alr, appreaciate it zyb

#

Also @polar mortar could u help on a similar question?

polar mortar
#

sure

uncut maple
#

the best way for you to understand my question would be for you to solve it first

#

its a simple one, but it'll make more sense if u do it

polar mortar
#

isn't this a trig sub?

uncut maple
#

Yep, exactly that, but theres something bugging me

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Well if just say x = sec(theta) and solve it, u'll get arcsec(x)

polar mortar
#

sounds about right, yeah.

uncut maple
#

I supposed 0 < theta < pi/2 U pi < theta < 3pi/2 so we have a inverse function, great

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In this case it didnt say arcsec(|x|) because it already defined x > 1 implicitly

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But why the restriction to the positive, why not simply arcsec(x) but rather arcsec(|x|)

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Another example from a similar trig sub. In this case 0 < theta < pi/2 U pi < theta < 3pi/2

polar mortar
#

without having solved it, I'm going to guess they get a sqrt(x^2) in there which is |x|. But, as you said, you already need x>1, so the absolute value is redundant.

uncut maple
#

yeah the absolute value is redundant because it already considered x > 1

#

,w derivate arcsec(x)

uncut maple
#

Which would make sense, the |x|

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But is there anyway I could figure that out without deriving my final answer?

polar mortar
#

you should be able to by looking at the domain and range of arcsec(x), that's where I'd start anyway.

uncut maple
#

well 0 < theta < pi/2 U pi < theta < 3pi/2

#

range x < -1 or x > 1 in this case

#

maybe because the function is odd?

polar mortar
#

maybe. I'm not sure. because now that I think about it, you don't need x>1, you need x>1 or x<-1 for the integral to be defined. Which is what secant does anyway. I'm not sure why they used |x| because it doesn't seem necessary.

uncut maple
#

Yeah, that's what im saying, but if you do int from -2 to -1 using arcsec(x) instead of arcsec(|x|) u get it wrong

#

,w arcsec(-1) - arcsec(-2)

uncut maple
#

,w arcsec(1) - arcsec(2)

uncut maple
#

-pi/3 would be the actual value of it

polar mortar
#

cat_thonk yeah, that is a weird little quirk.

uncut maple
#

im not crazy thankfullyhype

polar mortar
#

this happens sometimes in stewarts book. It's likely a domain issue, or something like that.

uncut maple
#

Yeah but its not wrong

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I just don't know why arcsec(|x|)

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oh actually mb, you have to do the improper int to -1 bc it has a infinite discontinuity

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but the idea still remains, like

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-3 to -2

polar mortar
#

oh. It's being wildly pedantic.
when you sub in you get
$$\frac{\sec\theta \tan\theta}{\sec\theta \sqrt{\sec^2\theta - 1}} = \frac{\sec\theta \tan\theta}{\sec\theta |\tan\theta|}$$

grand pondBOT
#

Zybikron

polar mortar
#

Which is +-1, the derivative of |theta|... maybe

uncut maple
#

yeah, since 0 < theta < pi/2 U pi < theta < 3pi/2, tan(theta) is always positive

#

one of the benefits of defining sec(x) for (0, pi/2) U (pi, 3pi/2)

#

I thought myb

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idk honestly

#

if u use u = sqrt{x^2 - 1} you get in terms of arctan

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,w \int \frac{1}{x\sqrt{x^2-1}}

uncut maple
#

then the problem wouldnt exist but

#

yeah

midnight plankBOT
#

@uncut maple Has your question been resolved?

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twilit field
#

Maybe I'm just too tired, but why isn't this 60

twilit field
#

it's a+<15> basically,right

runic hamlet
#

sure

#

what are the elements of 7+<15>?

wispy mortar
#

dont we have a direct formula for this

twilit field
#

oh right

#

These are basically translates

#

so 4 it is

twilit field
runic hamlet
#

correct brackets please

#

you arent first year

#

these mistakes are embarrassing

runic hamlet
twilit field
#

{22, 37, 52,7}, {16,31,46,1},{15,30,45,0},{2,17,32,47}

#

I just realised there can be more

#

The order of <15> is 4, And o(Z_60)=60

#

so we have 15 cosets

runic hamlet
#

yes

twilit field
#

cool

#

thanks

#

.close

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floral ruin
#

guys I wanted to know if there is a method where I can solve this using calculus.

floral ruin
#

like somehow can i find out the points on both the functions where the slops are same?

woeful turret
potent knoll
#

Differentiate the curves and find the general equation

woeful turret
floral ruin
slow thorn
#

you could use line equation in parametric form if you know that

#

$yt = x + at^2$ for a tangent passing through $(at^2, 2at)$ for a parabola $y^2 = 4ax$

grand pondBOT
floral ruin
#

i solved it using y=mx+a/m and then applied distance formula from the centre of the circle

slow thorn
#

yeah that too

floral ruin
#

What about this one?

#

I drew a rough sketch of the graph

potent knoll
floral ruin
#

the approach

#

how should I tackle this one?

#

should I just assume parametric coordinates for P and Q and then continue with the algebra of centroid?

potent knoll
floral ruin
potent knoll
floral ruin
#

yea

potent knoll
#

Then you should be able to relate them through sum of coordinates to the line eq

floral ruin
#

alright lemme try

#

done

#

thanks!

#

.close

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onyx tide
#

Can anyone check this before I proceed?

midnight plankBOT
bold peak
#

Yup looks good

onyx tide
#

100% sure?

bold peak
#

As much as I can reasonably be

onyx tide
#

Fine then

clever sedge
#

Just put everything in one line, as it's clearly possible 🙃

#

As in x^4 + x^6 could easily be on the third line together with the rest of the terms

#

Makes reading much easier

midnight plankBOT
#

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onyx tide
#

.close

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woeful turret
midnight plankBOT
lyric charm
#

holy shit the font sizes 😭😭

woeful turret
#

i was thinking since the function is strictly increasing, f(5x)/f(x) =1 when x-->infinity so ans = 0

#

but is it really meant to be that easy?

#

or am i missing something

lyric charm
#

well you have $1 \leq \frac{f(5x)}{f(x)} \leq \frac{f(7x)}{f(x)}$

grand pondBOT
woeful turret
#

hm why will it be >=1

#

oh nvm

#

ohh ok got it

#

thanks

#

.close

midnight plankBOT
#
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tall crag
#

In the game of Two-Finger Morra, 2 players show
1 or 2 fingers and simultaneously guess the number
of fingers their opponent will show. If only one of
the players guesses correctly, he wins an amount(in dollars) equal to the sum of the fingers shown
by him and his opponent. If both players guess
correctly or if neither guesses correctly, then no
money is exchanged. Consider a specified player,
and denote by X the amount of money he wins in
a single game of Two-Finger Morra.
(a) If each player acts independently of the other,
and if each player makes his choice of the
number of fingers he will hold up and the
number he will guess that his opponent will
hold up in such a way that each of the 4 pos-
sibilities is equally likely, what are the possi-
ble values of X and what are their associated
probabilities

tall crag
#

i didnt understand how the game works

obsidian anvil
#

pick a number, either 1 or 2

#

and then guess the number your opponent picks, either 1 or two

#

does it make sense how there are 4 outcomes?

obsidian anvil
#

so what would each outcome be

tall crag
#

{1,2}x{1,2}

obsidian anvil
#

yes

tall crag
#

mhm

obsidian anvil
#

now we know that each possibility is equally likely right

#

because they choose independently of one another

tall crag
#

yes

obsidian anvil
#

i think u get it u just needed the game itself to be further elaborated

tall crag
#

yeah thanks bro

obsidian anvil
#

i’m assuming part b asks for expected value

tall crag
#

no

obsidian anvil
#

oh

#

well just remember that X is the amount of money you can win

tall crag
#

Suppose that each player acts independently
of the other. If each player decides to hold up
the same number of fingers that he guesses his
opponent will hold up, and if each player is
equally likely to hold up 1 or 2 fingers, what
are the possible values of X and their associ-
ated probabilities?

obsidian anvil
#

so what are the possible values for X

tall crag
tall crag
obsidian anvil
#

yes but it might help to think about what values X can take on

tall crag
obsidian anvil
#

because ultimately you’re finding P(X=0), P(X = 7) etc

obsidian anvil
#

think about the outcomes where X ≠ 0

tall crag
obsidian anvil
tall crag
obsidian anvil
#

oh wait can u hold up no fingers

#

no u can’t

tall crag
obsidian anvil
#

I lied x can be 2

#

if you hold up 1 and ur opponent holds up 1

obsidian anvil
#

so now we have to find out the prob. of each outcome

#

the way i might do it is figure out how many diff ways you can get each value or X, sum them, and then do naive probability

#

easiest to start top down

#

how many ways can X = 4

tall crag
#

for all

#

its symmetric

obsidian anvil
#

yup

#

X = 3?

tall crag
#

for X = 2, 4, 3

#

all 1

#

wait

obsidian anvil
#

arent there multiple ways to win 3 dollars

tall crag
#

X=3 is 2

#

i think

obsidian anvil
#

i think so too

#

and by similar logic, x=2 is also 2 outcomes

tall crag
#

hm ye

#

no

#

its 1

obsidian anvil
#

yes

#

my bad

tall crag
#

lol

obsidian anvil
#

bc outcomes are 11, 12, 21, 22

tall crag
#

yes

#

2 wait

#

so for

obsidian anvil
#

2, 3, 3, 4

tall crag
#

X=0

#

we have how many ways?

obsidian anvil
#

let me think

#

it’s smth like all the ways where your guess ≠ your opponents hand or where they are equal

#

bc it’s 0 if either both guess incorrectly or both guess correctly right

tall crag
#

P(X=0) = 1 - sum(P(X=i)) , i = 2,3,4 right?

obsidian anvil
#

yup

tall crag
#

so what is the whole outcomes?

obsidian anvil
#

that’s why we’re trying to find |x=0|

tall crag
#

look

#

we should take one guess and bring either 1 or 2 fingers

#

right?

#

each player can do it tho

#

so its just |{guess,finger}|^2

obsidian anvil
#

wouldn’t it just be the probability that your guess is not equal to your opponents hand

obsidian anvil
tall crag
#

so its like

#

we bring 2 fingers up either 1 or 2 and take 2 guessues

#

so the cartesian would be 4^2

#

= 16 ways

#

now we have probs for X = 2,3,4

#

so sum of them is 3 * 1/16

#

1 - 3/16 = 13/16

#

@obsidian anvil i think we got part a

#

oh wait

#

its 4/16

#

i forgot X = 3 has. outcomes

obsidian anvil
#

and then the same for all the other ones, just find the prob

midnight plankBOT
#

@tall crag Has your question been resolved?

tall crag
obsidian anvil
tall crag
obsidian anvil
#

the w asks for each value of x and its probability

obsidian anvil
tall crag
obsidian anvil
#

x cant = 1

tall crag
tall crag
tall crag
midnight plankBOT
#

@tall crag Has your question been resolved?

#
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#
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pale osprey
midnight plankBOT
pale osprey
#

Very simple and silly question I know but

#

I did 3/2 x 160 and got 240 ml for this but the answer is 540ml idk what I missed

lusty python
#

you dare steal my name

lusty python
outer saffron
gaunt jetty
#

it scales by a factor of k^3

pale osprey
#

How would I do that again? I’m helping my sibling out and literally forgot

#

💀

lethal path
#

volume ratio = (length ratio)^3

lusty python
gaunt jetty
#

just cube the scaling factor you found

pale osprey
#

Same with this I got 1080g but the answer is 750g

lusty python
#

let the volume be $l$

grand pondBOT
#

1 divided by 0 equals Infinity

pale osprey
lusty python
#

so we got an equation $\frac{14}{160} = \frac{21}{l}$

grand pondBOT
#

1 divided by 0 equals Infinity

lusty python
#

simplest way to understand

outer saffron
wooden badger
#

or you could do longer by actually making equations of volumes

lusty python
outer saffron
wooden badger
lusty python
wooden badger
#

she did the same i believe

pale osprey
#

The answer is 540

outer saffron
gaunt jetty
#

,calc 160*3.375

grand pondBOT
#

Result:

540
pale osprey
outer saffron
wooden badger
pale osprey
outer saffron
wooden badger
#

this would be the longer method

#

ignore my camera quality i prob need a new phone

lofty knoll
#

1.20 * standard box = 900 so special is 750

outer saffron
# pale osprey

Lets form the equation properly ,we have 120 percent of a variable Xwhich gives 900,meaning (120/100)×X=900

pale osprey
#

120%=900

#

100%= (20% of 900) - 900

#

720

outer saffron
#

Percentagws dont work that way

pale osprey
lusty python
#

let $x$ be such that $120% \cdot x = 900$

grand pondBOT
#

1 divided by 0 equals Infinity

lusty python
#

so if you want to find $100%$, then go find $x$ yourself

grand pondBOT
#

1 divided by 0 equals Infinity

lusty python
#

@pale osprey

#

that's the trick for you to remember how

pale osprey
#

Thank u very much!

midnight plankBOT
#

@pale osprey Has your question been resolved?

midnight plankBOT
#
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#
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wicked mauve
#

i have the curl

midnight plankBOT
wicked mauve
#

i dont know what do to since its a cube

unreal finch
wicked mauve
#

<1,0,-x>

#

there

unreal finch
#

shoot, ive just had my multivariable exam, stokes theorm can indeed be tedious

#

you do know how to solve a surface integral tho right?

wicked mauve
#

😂

#

i have even more troubles with it lol

#

ever since we started going over line and surface integrals ive lost an understanding in what we're doing in class

unreal finch
#

ah well in our case youd have to verify the line integral and the corresponding greens theorm equivalent as proof, it messed me up

#

the thing about stokes is that you just need to "choose" a convenient surface

wicked mauve
#

good golly

#

😭

#

i am cooked

#

idk what to choose for the surface here

#

and idk how to get ru and rv

unreal finch
wicked mauve
#

i really have no clue what that means

#

my prof doesnt use the normal vector

#

well explicitly

unreal finch
#

but good hting im done with that sem

wicked mauve
#

my final is on saturday

#

and there is gonna be an frq on stokes surely

#

but the thing is the homework is so much more difficult

#

so i have no clue how to do this

#

the textbook doesnt help and my prof only does problems from the textbook lol

thorn crown
#

Since it's telling you to use Stokes's theorem should you be trying to calculate a certain line integral?

unreal finch
wicked mauve
thorn crown
#

What do you mean you're trying to do a surface?

wicked mauve
#

isnt what what stokes is

#

a line integral into a surface

thorn crown
#

It can also be viewed as a surface integral into a line integral

wicked mauve
#

oh yeah

#

the reverse

#

so what would i do

thorn crown
#

Stokes's theorem doesn't directly hold here but you can show that Stokes's equation will be true nonetheless for this problem by considering each face of the cube separately and you will see certain line integrals (remembering the orientation rules of the theorem) cancel such that you can calculate it as the line integral around the "base" on the xy-plane

#

I'm not too sure how familiar you are with Stokes's theorem so I tried to include extra details

wicked mauve
#

so it is a line integral of a square

thorn crown
#

Yes

#

My quick calculations had three of the four line integals being zeroes

wicked mauve
#

what would i do to do them line integrals

#

oh

#

nvm

thorn crown
#

You would calculate them like you normally would

wicked mauve
#

okay let me try

wicked mauve
thorn crown
#

What is "it"? I assume you are referring the boundary of the square on the xy-plane described by 0<= x <= 1, 0 <= y <= 1

wicked mauve
#

well tbh im not really sure myself

thorn crown
#

Ok.

wicked mauve
#

but in my notes i have

#

hang on

thorn crown
#

Ok

#

I will try and use paint to draw a graph so you can see precisely what I'm trying to describe

wicked mauve
#

this

#

or is this not the same

#

that is equal to the line integral of F dot dr

thorn crown
#

It is equal to that if the curve is "nice" yes

wicked mauve
#

i am still stuck

thorn crown
#

My diagram has gone a bit crazy

wicked mauve
#

its okay

thorn crown
#

It's not got the back faces stuff but this is the idea I was trying to say with words and this is why you end up with only the line integral over the base as all the other cancel

wicked mauve
#

okay i understand that part

#

what a nice cube

thorn crown
#

So we want to calculate the line integral over this which I have split into four

wicked mauve
#

can i do any line integral?

thorn crown
#

Yes we will need to do all four over these four curves

#

We desire

wicked mauve
#

or it has to be

thorn crown
#

$\int_{c_1} xy \dd{x} - z \dd{y} + ... + \int_{c_4} xy \dd{x} - z \dd{y}$

grand pondBOT
#

stabulo

wicked mauve
#

oh okay

#

so

thorn crown
#

We will need to come up with four paramaterisations for each c_i

wicked mauve
#

greens theorem

#

no

#

yes?

thorn crown
#

For c_1:

#

x needs to go from 0 to 1 in a linear way

#

The obvious choice would be x = t

#

We can see from the graph that y = 0 over the entire segment c_1

#

c_1: x = t, y = 0, 0 <= t <= 1

#

This is the easiest one to do but you should try to extrapolate this logic to c_2, ..., c_4

wicked mauve
#

so for c2 x=0 and y=t?

thorn crown
#

Close

wicked mauve
#

oh

thorn crown
#

But x = 1 over the entirety of c_2

wicked mauve
#

x=1

thorn crown
#

Yes

#

I'll give you this trick ahead of time

#

But say if instead we needed to go from x = 0 to x = 2 it's best to use x = 2t so we can keep is having 0 <= t <= 1

#

This is because the eventual integral we end up with is almost always easier if the bounds are 0 to 1

wicked mauve
#

ah okay

#

that makes sense

thorn crown
#

So far we have
c_1: x = t, y = 0, 0 <= t <= 1
c_2: x =1, y = t, 0<= t <= 1

#

Just two more

wicked mauve
#

and then c3: x=-t y=1

#

and c4: x=0, y=-t ?

thorn crown
#

Are you using the same 0 < = t <= 1?

wicked mauve
#

yes

thorn crown
#

If so c_3 looks wrong

#

and c_4

wicked mauve
#

oh

#

😩

#

dang

thorn crown
#

This is because you will, for c_3, start at x = 0 and end at x = -1

#

You want to start at 1 and end at 0

#

x = ?

wicked mauve
#

oh so x=t ?

#

y=1

thorn crown
#

No

#

x = 1 - t

#

This starts at x = 1 and ends at x = 0

wicked mauve
#

ohhhhh

#

okay that makes sense

#

😭

#

damn

thorn crown
#

This one is more of a thing where you need to see it at least once before to be fair

#

c_4 will have a similar paramaterisation trick

wicked mauve
#

okay then c4: x=0, y=1-t

thorn crown
#

Yes

#

So we have
c_1: x = t, y = 0, 0 <= t <= 1
c_2: x =1, y = t, 0<= t <= 1
c_3: x = 1 - t, y = 1, 0 <= t <= 1
c_4: x = 0, y = 1 - t, 0 <= t <= 1

thorn crown
wicked mauve
#

is the z irrelevant here?

thorn crown
#

You should see many are zeroes quickly especially since z = 0 everywhere

wicked mauve
#

okay

thorn crown
wicked mauve
#

gotcha

#

thats basicallyyyy what i meant lol

thorn crown
#

$\int_{c1} xy \dd{x} + ... + \int_{c_4} xy \dd{x}$

wicked mauve
#

okay let me try

grand pondBOT
#

stabulo

wicked mauve
#

would it be wrong to make them all 1 integral?

#

since its addition

#

now im confused

thorn crown
#

x will have different values in each of them

#

You could eventually I suppose when everything is in terms of t

#

But you will see quickly the line integrals over three of the four are zeroes fast

#

Either because x, y or dx = 0

wicked mauve
#

can you help me with c1

thorn crown
#

Yes

wicked mauve
#

okay thank you

thorn crown
#

c_1: x = t, y = 0, 0 <= t <= 1

wicked mauve
#

i just plug them in?

thorn crown
#

Essentially, yes.

wicked mauve
#

ohhh okay

thorn crown
#

x = t, y = 0 and dx = dt

wicked mauve
#

so 0

thorn crown
#

Yes

wicked mauve
#

c4 is 0 also

thorn crown
#

I agree with that

#

The only non-zero one I find is the line integral over c_2

wicked mauve
#

is the answer 1?

thorn crown
#

I don't think so but why do you?

wicked mauve
#

for why isnt c3 nonzero

wicked mauve
thorn crown
#

c_3 is zero I think

wicked mauve
#

the integral would be t- 1/2 t^(2)

#

no?

thorn crown
#

Yes you're right

#

I mixed up c_2 and c_3

#

But I don't get the value to be 1 for this integral

#

I get -1/2

wicked mauve
#

let me show what i did

#

hang on

thorn crown
#

Ok 🙂

wicked mauve
#

thats for c3

thorn crown
#

dx = - dt is the difference since x = 1 - t

#

So the actual line integral will equal - 1/2

wicked mauve
#

how did you get dt though

thorn crown
#

If x = 1 - t then dx = (dx/dt) dt but dx/dt = -1

wicked mauve
#

ohh

#

okay i see

#

yes

#

so

#

then i get 0?

#

overall

thorn crown
#

No

#

What do you get for c_4?

wicked mauve
#

0

#

for c2 i gto 1/2

thorn crown
#

So why would the sum of 0, 0, - 1/2 and 0 be 0?

wicked mauve
#

i got 0 + 1/2 -1/2 + 0

thorn crown
#

Since x = 1

wicked mauve
#

oh

#

okay

#

i see now

#

so overall -1/2 is the answer then

thorn crown
#

Yes I think so

wicked mauve
#

you're a genius

#

okay can you help me with another one?

thorn crown
#

I've been studying this stuff more carefully lately is all

thorn crown
wicked mauve
#

ill show you and mayhaps you can

thorn crown
#

First try applying what you've learnt here

wicked mauve
#

i will try

#

i am just confused by the wording maybe

#

ok hang on

wicked mauve
#

woudl they be the same ?

thorn crown
#

Probably not the easiest problem if new

wicked mauve
#

answer

thorn crown
#

What did you get?

wicked mauve
#

36pi

thorn crown
#

I get 63 pi

wicked mauve
#

they would be the same no?

thorn crown
#

Yes both answers should be the same as you are verifying the theorem for a particular problem

wicked mauve
#

makes sense

#

which one did you do

#

A?

thorn crown
#

I did the surface integral

wicked mauve
#

well i dont want the problem to reset so ill show my work

#

hang on

thorn crown
#

Ok

#

I get 63 pi for the line integral path too so not sure what's making the difference

#

The surface integral path is much more tricky

wicked mauve
#

hopefully its legible

thorn crown
#

I get a different curl

#

I get <2, 4, 7>

wicked mauve
#

hm

#

okay hang on

#

fuck

thorn crown
#

That error propagates but is a quick fix

wicked mauve
#

i wrote 4x instead of 7x

#

😭

thorn crown
#

Happens 🙂

wicked mauve
#

what is even society

#

okay well

#

i will try the line integral now

thorn crown
#

Once that is fixed you should get 63 pi

wicked mauve
#

does it have to be in t?

#

oh wait

thorn crown
#

Doesn't have to be t

#

Any paramaterisation variable works

wicked mauve
#

can i do x = rcos theta?

#

but then thats 2

#

things

thorn crown
#

This is the obvious choice, yes.

#

Can even say x = r cos(t)

wicked mauve
#

and then that will be r(t)

#

and then i differentiate them

#

?

thorn crown
#

r(t) = < 3 cos(t), 3 sin(t), 0>

wicked mauve
#

okay

#

okay i got it blankstare

#

wow

thorn crown
#

Nice 🙂

wicked mauve
#

i feel my neurons

#

thank you for all your help

#

i really appreciate it

thorn crown
#

Glad to help

wicked mauve
#

too kind i wish you nothing but the best

#

thank you

#

.close

midnight plankBOT
#
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midnight plankBOT
#
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dreamy prairie
midnight plankBOT
#

Please don't occupy multiple help channels.

astral canyon
#

.close there's already an open channel

midnight plankBOT
#
Channel closed

Closed by @astral canyon

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dreamy prairie
#

wow

#

thanks for your help bro

#

appreciate you

midnight plankBOT
#
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tall crag
#

Suppose that two teams play a series of games that
ends when one of them has won i games. Suppose
that each game played is, independently, won by
team A with probability p. Find the expected num-
ber of games that are played when (a) i= 2 and (b)
i= 3. Also, show in both cases that this number is
maximized when p= 1/2

tall crag
#

for i = 2 i said $P(2) = p^2 + (1-p)^2$ and $P(3) = 1-P(2) = 2p(1-p)$ is that right?

grand pondBOT
#

Viͥђaͣnͫ

visual tiger
#

probability that x games are played?

#

it looks good

tall crag
tall crag
# visual tiger it looks good

i computed $\mathbb{E}[X]$ and got $2+2p(1-p)$ then i took the derivative and got $\frac{d}{dp} \mathbb{E}[X] = 2p(1-p) = 0 $ hence $p* = 1/2$

grand pondBOT
#

Viͥђaͣnͫ

tall crag
#

but idk what to do for when i = 3

visual tiger
tall crag
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why

visual tiger
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how do you take the derivative of 2p(1-p)

tall crag
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wait yes sorry

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2(1-2p)

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i wrote it wrong

tall crag
visual tiger
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how would you have that

tall crag
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sorry i meant P(3)

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not EX

visual tiger
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yes P(X=3) is that

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we can keep going a bit

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what are the other possible values of X

tall crag
#

X=4,5 right?

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bc if

visual tiger
#

yes

tall crag
#

we hit 5

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it either be draw

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sorry

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either lose or win

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so like

visual tiger
#

maybe X = 5 is easier to understand

tall crag
#

X = 4 idk

visual tiger
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what happened if X = 5

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what happened to the first 4 games

tall crag
visual tiger
#

ok

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so 5th game can either be lose or win, we don't care

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1st-4th games are 2 wins, 2 losses

tall crag
#

C(4,2) p^2 (1-p)^2 right?

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binom

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so

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for X=4?

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can we sum up

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and 1 - sum?

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that would be hard to compute

visual tiger
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it's 3 terms, you don't need to expand

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all we care about is solving dE/dp = 0 in the end

tall crag
#

hmmm

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am calculating

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4 - P(3) + P(4)

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$\mathbb{E}[X] = 4 - (p^3 + (1-p)^3) + 6 p^2 (1-p)^2$

grand pondBOT
#

Viͥђaͣnͫ

tall crag
#

$\frac{d}{dp} P(3) = 3p^2 + 3(1-p)^2(-1) = 3p^2 - 3(1-p)^2$ and $\frac{d}{dp} P(5) = 12 p(1-p)^2 - 12 p^2 (1-p)$

grand pondBOT
#

Viͥђaͣnͫ

tall crag
#

$\frac{d}{dp} \mathbb{E}[N] = - (3p^2 - 3(1-p)^2) + \big(12 p(1-p)^2 - 12 p^2 (1-p)\big)$

grand pondBOT
#

Viͥђaͣnͫ

tall crag
#

bruv

visual tiger
#

wait a bit

visual tiger
tall crag
#

calculating this

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i simplified it a bit

visual tiger
tall crag
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$\frac{d}{dp} \mathbb{E}[N] = (1-2p)\big(3 + 12p(1-p)\big)$

grand pondBOT
#

Viͥђaͣnͫ

tall crag
#

so just 1-2p = 0 so p* = 1/2

visual tiger
tall crag
visual tiger
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you need to show why you can't have 3 + 12p(1-p) = 0

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well it's easy

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but small bit to show you saw that

tall crag
visual tiger
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what tells you that 1/2 is the max

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and not that other critical point

tall crag
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hm

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ok ig i found it out

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p(1-p) = -3/12 which is impossible

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im so dumb

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smh

honest jasper
tall crag
#

@visual tiger thx bruv 🫂

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.close

midnight plankBOT
#
Channel closed

Closed by @tall crag

Use .reopen if this was a mistake.

midnight plankBOT
#
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brittle cedar
#

can someone help with the ticked numbers? start with 4 pls

brittle cedar
#

how do I start 4

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are these 2 triangles the same?

wooden badger
#

No not necessarily

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@brittle cedar

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Try to equate alternate interior angles

brittle cedar
#

is the 100 angle the same with T?

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am i correct @wooden badger

wooden badger
#

Yes

brittle cedar
#

ok

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im guessing r and s = 40?

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@wooden badger

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mb for pinging

wooden badger
#

Yep

brittle cedar
#

wait but how

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they're not marked congruent though

wooden badger
#

S and b do u think they'd be equal?

brittle cedar
wooden badger
#

Angle s and B

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Ive marked them

brittle cedar
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4

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ok anyways

wooden badger
brittle cedar
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OH

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ok

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so and B?

wooden badger
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Yes

brittle cedar
#

is b referring to the outside or insied

wooden badger
#

The angle thts marked in the diagram

brittle cedar
#

yeah

wooden badger
#

So they're equal ryt?

brittle cedar
#

yea

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because of corresponding?

wooden badger
#

Co exterior angles

brittle cedar
#

what's that

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i dont think we were taught that

wooden badger
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Wait no what r they called

brittle cedar
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consecutive????

wooden badger
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Yeah corresponding you're right

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R is equal to a

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@brittle cedar can u see how

brittle cedar
#

i mean

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the A doesn't look like an A

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that's why i got confused

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anyways thanks