#help-49
1 messages · Page 263 of 1
Bruh.
Yes.
should I just matrix this lol
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Turu
u a jee guy?
is the result perhaps
$\frac{\ln(x-1)}{2}-\ln(x-2)+\frac{ln(x-3)}{2}$
Yes.
laestia
unless I'm dumb
Lemme calculate.
the pfd results is 1/2(x-1)-1/(x-2)+1/2(x-3)
Uhh, i gor both the 2's on the numerator.
OH WAIT.
No.
On the denominator.
Yeah.
so ts is correct right
Yes.
Yes.
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#help-21|아리스킨충1 is currently open by the way
I sent it there
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is there any other way to do this without assuming ϴ = 90°
AM>=GM inequality.
Note that cosec = 1/sin, solve the quadratic in sine-theta, and evaluate the desired value
This would also work, assuming you know what that inequality is
only applies when the terms are non-negative
that too
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x + 1/x always greater than or equal to 2
x = -1:
yes for positive numbers
is sin x always positive then
for negative it is -2 to - inf
i mean
its obv
that u wont get 2
if sin takes a negative value
so i didnt bother
hi
u got doubt in this?
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oh nvm
...
you can close the channel with .close
lol
.close
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Whatt
Close
.close
.close
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a guess is that maybe if the two curves intersect f(x)=x at the same two points something is …
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someone help me differentiate this i keep getting it wrong
And you aim to differentiate with respect to...?
What have you tried, if anything?
@vast citrus this channel is for helping zah with her geometry homework. please keep it on topic
Wrong place, and I could swear this has been done multiple times.
Can you spot this as a product?
Wait hold on, not even that
You're differentiating with respect to PHI, right?
yeah and so the other terms are constant
Then the whole part before the cosine-reciprocal thing, relative to PHI, is just a constant, yh
why is it just a constant?
Because nothing there depends on phi
Wrong server sorry
And where here does the tangent function even appear?
cant you combine sin and cos
No?
That'd only apply if the arguments of both the sine and cosine matched
But they DON'T match
But this, essentially
I don't quite agree that this is the derivative of that section btw
oh
The Chain Rule applies here too, so you have to multiply this result by the derivative of cos(phi - theta) [with respect to phi]
yeah
So the outer function (the -1 power), that derivative was fine
The inner function is cos(phi -theta)
What's the deriv. of cosine?
-sine
@leaden seal
yee
Now multiply that with that ^-2 thing and the coefficient of that original cosine (that is, the w sin() thing)
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@tidal turret Has your question been resolved?
@tidal turret Has your question been resolved?
@tidal turret Has your question been resolved?
@tidal turret Has your question been resolved?
did you learn lagrangian?
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
start by finding all candidate optimizers (gradient = 0, which translates into 3x^2 - 2y = 0)
then check each boundary seperately
the harder one is $1/2 x^2 + 1/4 y^2 = 1$
king of complex analysis
thats what i get for not using \frac
anyway
isolate for y^2
$y^2 = 4(1 - \frac{1}{2}x^2$
$y^2 = 4(1 - \frac{1}{2}x^2)$
king of complex analysis
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)
then repeat with the other boundary
how
\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 }.
]
Renato
draw.
Hey Renato
hey
Still having trouble with the problem?
yes
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?
@tidal turret Has your question been resolved?
@tidal turret é brasilieiro?
the original equation has y^2
like, the thing to find the extrema of
replace y^2 with the other half of this
easier to do it this way because there is no square root business, isolating x is harder
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hi can someone help idk how to integrate this
if you do integration by parts, can you get the sqrt into the denominator?
oh i thought that would make it look like the derivative of arcsin, but the sign is wrong
i think your simplification went wrong somewhere along the way
yeah i think the u-sub is not working
you didn't change the limits when you did the u-sub
i think you can substitute u = t - pi
on the fifth line
then you get an odd function
What's the original question?
,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
Axe
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please help
I think you can make an argument for 1/3 based on symmetry
Like you can partition the space of orders based on the equivalence relation that permutes the triplets
can you give an example i don't really understand what you mean by that
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
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yea cane someone do this for me i aint tryna do all that
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i know i know
i just think its stupid to set such a qwuestionb
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Also stupid to share just to complain
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$\int \frac{1}{1+\cos{x}}$
felipe
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
prob a stupid question but i have to ask it lol
when you do this you generally (implicitly) assume you're excluding values where you divide by 0
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?
sure
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
isn't this a trig sub?
Yep, exactly that, but theres something bugging me
Well if just say x = sec(theta) and solve it, u'll get arcsec(x)
sounds about right, yeah.
I supposed 0 < theta < pi/2 U pi < theta < 3pi/2 so we have a inverse function, great
In this case it didnt say arcsec(|x|) because it already defined x > 1 implicitly
But why the restriction to the positive, why not simply arcsec(x) but rather arcsec(|x|)
Another example from a similar trig sub. In this case 0 < theta < pi/2 U pi < theta < 3pi/2
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.
yeah the absolute value is redundant because it already considered x > 1
,w derivate arcsec(x)
Which would make sense, the |x|
But is there anyway I could figure that out without deriving my final answer?
you should be able to by looking at the domain and range of arcsec(x), that's where I'd start anyway.
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?
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.
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)
,w arcsec(1) - arcsec(2)
-pi/3 would be the actual value of it
yeah, that is a weird little quirk.
im not crazy thankfully
this happens sometimes in stewarts book. It's likely a domain issue, or something like that.
Yeah but its not wrong
I just don't know why arcsec(|x|)
oh actually mb, you have to do the improper int to -1 bc it has a infinite discontinuity
but the idea still remains, like
-3 to -2
oh. It's being wildly pedantic.
when you sub in you get
$$\frac{\sec\theta \tan\theta}{\sec\theta \sqrt{\sec^2\theta - 1}} = \frac{\sec\theta \tan\theta}{\sec\theta |\tan\theta|}$$
Zybikron
Which is +-1, the derivative of |theta|... maybe
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
idk honestly
if u use u = sqrt{x^2 - 1} you get in terms of arctan
,w \int \frac{1}{x\sqrt{x^2-1}}
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Maybe I'm just too tired, but why isn't this 60
it's a+<15> basically,right
dont we have a direct formula for this
{22, 37, 52,7}
oh right
These are basically translates

so 4 it is
yup, number of cosets
yes but no
correct brackets please
you arent first year
these mistakes are embarrassing
what are the 4 elements of the group?
{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
yes
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guys I wanted to know if there is a method where I can solve this using calculus.
like somehow can i find out the points on both the functions where the slops are same?
Yes, you're able to
hmm if u equate the slopes ull only get one equation tho
Differentiate the curves and find the general equation
calculus is a bad approach for this question..just use standard form of tangent for both these curves
ohh
ohh i see. Was just curious if that would work better but thanks!
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 $y^2 = 4ax$
i solved it using y=mx+a/m and then applied distance formula from the centre of the circle
yeah that too
yeaa
What about this one?
I drew a rough sketch of the graph
What exactly are you confused about on this?
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?
In general?
yea or like any method
You can find the focus of the parabola and set up the centroid eq
yea
Then you should be able to relate them through sum of coordinates to the line eq
Yep
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Can anyone check this before I proceed?
Yup looks good
100% sure?
As much as I can reasonably be
Fine then
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
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.close
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holy shit the font sizes 😭😭
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
well you have $1 \leq \frac{f(5x)}{f(x)} \leq \frac{f(7x)}{f(x)}$
Ann
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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
i didnt understand how the game works
essentially each player has two tasks
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?
so what would each outcome be
{1,2}x{1,2}
yes
mhm
now we know that each possibility is equally likely right
because they choose independently of one another
yes
i think u get it u just needed the game itself to be further elaborated
yeah thanks bro
i’m assuming part b asks for expected value
no
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?
so what are the possible values for X
X = 0 if both are either correct or incorrect and X = i + j for i fingers up from the first person and j by the sec
only if the player guess correct tho
yes but it might help to think about what values X can take on
that'd be smth like 16?
because ultimately you’re finding P(X=0), P(X = 7) etc
X = 2, 4, 3
i don’t know if X can = 2
why not?
nope
yep
yes so x can be 0, 2, 3, 4
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
arent there multiple ways to win 3 dollars
lol
bc outcomes are 11, 12, 21, 22
2, 3, 3, 4
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
P(X=0) = 1 - sum(P(X=i)) , i = 2,3,4 right?
yup
so what is the whole outcomes?
that’s why we’re trying to find |x=0|
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
wouldn’t it just be the probability that your guess is not equal to your opponents hand
yes i think
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
that’s for x=1
and then the same for all the other ones, just find the prob
@tall crag Has your question been resolved?
X=1????
x=0 has p 12/16
Hm
the w asks for each value of x and its probability
isn’t that what u just solved lol
Didnt we say it for X=0
Yep
b part?
What would it be
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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
you dare steal my name
anyways
Not only the height but the base also increases in size so its isnt just a 3/2 multiple
the volume doesnt scale by a linear factor
it scales by a factor of k^3
volume ratio = (length ratio)^3
goodness
just cube the scaling factor you found
Same with this I got 1080g but the answer is 750g
let the volume be $l$
1 divided by 0 equals Infinity
Ah ok
so we got an equation $\frac{14}{160} = \frac{21}{l}$
1 divided by 0 equals Infinity
simplest way to understand
The box with 900 grams is the bigger box they are asking you to find the original size
or you could do longer by actually making equations of volumes
like dis
Omg
🤦♀️
That was mb
Nw
wht r u even doing
isn't that forming the equation?
tht would give 240...
she did the same i believe
I got 360ml by doing this which is wrong
The answer is 540
No like you got 3/2, cube that and multiply it to 160
,calc 160*3.375
Result:
540
Bruh I got 720g when it’s 750
Try again i got 750
calculation mistake maybe
Oh nvm
Yeah just recalculate both the answeres and you should get it
1.20 * standard box = 900 so special is 750
Lets form the equation properly ,we have 120 percent of a variable Xwhich gives 900,meaning (120/100)×X=900
Nope that isnt how it works
Percentagws dont work that way
Other way around srry
1 divided by 0 equals Infinity
so if you want to find $100%$, then go find $x$ yourself
1 divided by 0 equals Infinity
Thank u very much!
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i have the curl
i dont know what do to since its a cube
what did you get as the curl
shoot, ive just had my multivariable exam, stokes theorm can indeed be tedious
you do know how to solve a surface integral tho right?
😂
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
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
good golly
😭
i am cooked
idk what to choose for the surface here
and idk how to get ru and rv
well theyve specified the faces use unit outward normal
i really have no clue what that means
my prof doesnt use the normal vector
well explicitly
me neither, i rly dont wanna confuse you with this further because of how difficult for me it is too 😭
but good hting im done with that sem
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
Since it's telling you to use Stokes's theorem should you be trying to calculate a certain line integral?
honestly stokes becomes pretty easy if youd just know how to solve a surface integral
yeah i feel you
im trying to do a surface but idk how 😭
What do you mean you're trying to do a surface?
It can also be viewed as a surface integral into a line integral
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
so it is a line integral of a square
You would calculate them like you normally would
okay let me try
what would i parameterize it as?
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
well tbh im not really sure myself
Ok.
Ok
I will try and use paint to draw a graph so you can see precisely what I'm trying to describe
It is equal to that if the curve is "nice" yes
i am still stuck
My diagram has gone a bit crazy
its okay
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
So we want to calculate the line integral over this which I have split into four
can i do any line integral?
or it has to be
$\int_{c_1} xy \dd{x} - z \dd{y} + ... + \int_{c_4} xy \dd{x} - z \dd{y}$
stabulo
We will need to come up with four paramaterisations for each c_i
You could actually, I never thought of that option
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
so for c2 x=0 and y=t?
Close
oh
But x = 1 over the entirety of c_2
x=1
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
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
Are you using the same 0 < = t <= 1?
yes
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 = ?
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
okay then c4: x=0, y=1-t
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
To will use this formula for each here
is the z irrelevant here?
You should see many are zeroes quickly especially since z = 0 everywhere
okay
z = 0 over the entire curve so really you can just get rid of it
$\int_{c1} xy \dd{x} + ... + \int_{c_4} xy \dd{x}$
okay let me try
stabulo
would it be wrong to make them all 1 integral?
since its addition
now im confused
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
can you help me with c1
Yes
okay thank you
c_1: x = t, y = 0, 0 <= t <= 1
i just plug them in?
Essentially, yes.
ohhh okay
x = t, y = 0 and dx = dt
so 0
Yes
c4 is 0 also
is the answer 1?
I don't think so but why do you?
for why isnt c3 nonzero
because i got c3
c_3 is zero I think
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
Ok 🙂
dx = - dt is the difference since x = 1 - t
So the actual line integral will equal - 1/2
how did you get dt though
If x = 1 - t then dx = (dx/dt) dt but dx/dt = -1
So why would the sum of 0, 0, - 1/2 and 0 be 0?
i got 0 + 1/2 -1/2 + 0
Yes I think so
I've been studying this stuff more carefully lately is all
I don't know
ill show you and mayhaps you can
First try applying what you've learnt here
okay so far i've only done part B
woudl they be the same ?
Probably not the easiest problem if new
answer
What did you get?
36pi
I get 63 pi
Yes both answers should be the same as you are verifying the theorem for a particular problem
I did the surface integral
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
That error propagates but is a quick fix
Happens 🙂
Once that is fixed you should get 63 pi
i am having troubles with the line integral
does it have to be in t?
oh wait
r(t) = < 3 cos(t), 3 sin(t), 0>
Nice 🙂
Glad to help
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Can u help me too
.close there's already an open channel
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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
for i = 2 i said $P(2) = p^2 + (1-p)^2$ and $P(3) = 1-P(2) = 2p(1-p)$ is that right?
Viͥђaͣnͫ
what is "P(2)" and "P(3)"
probability that x games are played?
it looks good
P(X=2), P(X=3) yes
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 $p* = 1/2$
Viͥђaͣnͫ
but idk what to do for when i = 3
uh wrong derivative
why
how do you take the derivative of 2p(1-p)
this
how would you have that
yes P(X=3) is that
we can keep going a bit
what are the other possible values of X
yes
maybe X = 5 is easier to understand
X = 4 idk
two games split and in 5th its either lose or win
ok
so 5th game can either be lose or win, we don't care
1st-4th games are 2 wins, 2 losses
C(4,2) p^2 (1-p)^2 right?
binom
so
for X=4?
can we sum up
and 1 - sum?
that would be hard to compute
it's 3 terms, you don't need to expand
all we care about is solving dE/dp = 0 in the end
hmmm
am calculating
4 - P(3) + P(4)
$\mathbb{E}[X] = 4 - (p^3 + (1-p)^3) + 6 p^2 (1-p)^2$
Viͥђaͣnͫ
$\frac{d}{dp} P(3) = 3p^2 + 3(1-p)^2(-1) = 3p^2 - 3(1-p)^2$ and $\frac{d}{dp} P(5) = 12 p(1-p)^2 - 12 p^2 (1-p)$
Viͥђaͣnͫ
$\frac{d}{dp} \mathbb{E}[N] = - (3p^2 - 3(1-p)^2) + \big(12 p(1-p)^2 - 12 p^2 (1-p)\big)$
Viͥђaͣnͫ
bruv
wait a bit
yeah ok this is good
you can factor the second big term by p(1-p)
$\frac{d}{dp} \mathbb{E}[N] = (1-2p)\big(3 + 12p(1-p)\big)$
Viͥђaͣnͫ
so just 1-2p = 0 so p* = 1/2
almost
warum
you need to show why you can't have 3 + 12p(1-p) = 0
well it's easy
but small bit to show you saw that
it just wanted us to show max is 1/2 so sure it doesnt
but if there's another critical point
what tells you that 1/2 is the max
and not that other critical point
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can someone help with the ticked numbers? start with 4 pls
ohhh
is the 100 angle the same with T?
am i correct @wooden badger
Yes
Yep
wdym
No thhts A lmao
Yes
is b referring to the outside or insied
The angle thts marked in the diagram
yeah
So they're equal ryt?
Co exterior angles
Wait no what r they called
consecutive????



