#help-42
1 messages · Page 81 of 1
your mom asked you to do this and you're not taking calculus?
why
differentiate x(t) twice and differentiate y(t) twice. no, I am mistaken
Why is that?
It's the chain rule
I'm not seeing a more nuanced answer than this so far:
Melvin Eugene Punymier
Disregard this ^
use such property:
that's what I was looking for
Ok wait let me read through everything
Yes, I see I was mistaken
Why was that wrong
bcz see this
$\frac{d^2 y}{dx^2} = {\frac{d}{dx} \left(\frac{dy}{dx}\right)} = \frac{d}{dt}\frac{dt}{dx}\left(\frac{dy}{dx}\right) = \frac{\frac{d}{dt}\left(\frac{dy}{dx}\right)}{\frac{dx}{dt}}$
Melvin Eugene Punymier
Bruh I thought dx^2 means d(x^2) 💀
what's the difference between dx^2 and d^2x?
I can't speak authoritatively on that
or rather, get the precise meaning
in context, d^2 y/dx^2 is the second derivative of y with respect to x
oh, lol
just look at the first two expressions
first derivative is just dy/dx
The derivative operator is d/dx
so we do d/dx (dy/dx)
and that's the wishy-washy part in my early calculus schooling
ok I kinda get that
a professor told me "we can basically multiply these but not really"
but that is effectively what happens!
we have two factors of d in the top, so d^2
and two factors of (dx) in the bottom, notated dx^2
yes
What does x(t) mean 💀
"x is a function of t"
What is the last two parts of the equalities for then
the penultimate expression shows that d/dx can be re-expressed as d/dt * dt/dx. The 'dx' parts cancel and we only have dt on the bottom
this is Chain Rule
the last part changes the way the penultimate expression is written. Instead of putting dt/dx on the top, we divide by dx/dt, which is equivalent.
this comes from what we already know about dividing or mulitplying by fractions
"dividing by a fraction is the same as multiplying by the recipricol of that fraction"
Isn’t there a dt/dx term tho
(in this case, we are doing the reverse direction of inference)
Yea I got that
^
? All the terms are there
Ok, did I confuse you by making it sound like we actually cancel something? We don't cancel. We need those terms there to get it in the form we want to end up with.
Effectively, it's the same as the factor we started with , d/dt
d/dx = (d/dt)(dt/dx)
the dx parts WOULD cancel
these expressions are equivalent
Isn’t d/dx*dx/dt=d/dt and not d/dx?
Ok so I get the steps but why would you do them?
I just fixed it up there too ^
to get dx/dt on the bottom
this part was always written correctly
Yea I followed it
What do you do with dx/dt?
$\frac{dt}{dx} = \frac{1}{\frac{dx}{dt}}$
Melvin Eugene Punymier
I get that it’s in the denominator but what do you do with it
we are able differentiate your x(t) with respect to t, so we can use this form to get the second derivative of y(t)/x(t)
What does respect to t mean?
have you ever differentiated an expression before?
because you don't seem familiar with function notation that's a distant precursor to calculus
Maybe not with proper notation
t is the variable we are doing calculus with. we are taking the limit of the function as changes in t become infinitesimally small.
although we are just leaning on some rules we memorized at this point, not actually taking limits
(though we could)
is this chain rule
Ok I get that
that is a derivative notation
I have been useing Leibniz notation
let's solve your problem
I’ve never actually done any calc questions, I’ve just seen people do it and I’m like ok the derivative of this is this
Ok yea
So what’s the step after this
Oh wait
So is dx/dt the derivative of x(t)
@bright lagoon
yes
here I am just using chain rule
you can see in the last step that we just need the second derivatve of y with respect to t
and the the square of the first derivative of x with respect to t
or, in other notation:
$\frac{y''(t)}{(x'(t))^2}$
Melvin Eugene Punymier
...which we can easily do
Ok I got it thanks!
Why is d^2y/dt^2 the second derivative of y(t)
Nvm
It’s d/dt *dy/dt
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little confused here
which part
All of it
first find the derivative, applying the relevant rules
Wouldnt it just be (43+31)’=0?
don't worry about the x=0 or the table
Oh
differentiate first then plug
otherwise you're essentially implying that the derivative evaluated anywhere for any function is 0
yes
to me i see (4(3) + 3(1))'
is this product rule stuff?
got it
just had to use my whiteboard lol
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How do you eval this limit?
@shrewd arch Has your question been resolved?
@shrewd arch Has your question been resolved?
<@&286206848099549185>
(?)
hm interesting limit ah
I mean I would guess it goes to 0
as a guess
lol
it goes to 1
I am not sure how you would evaluate this
I think there might be a way
hm
oh nvm I tought you could solve it with polylogarithms but nvm
@shrewd arch Has your question been resolved?
Riemann sums
I think you take it in university
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use riemann the limit equals to : integral 0 to 1 (x*e^x)dx
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I think it might be 42 cuz this is the only approach from which i could get a possibly definite answer
as since it's 8 so it's 16, then 7 so it should be 14 and 6 so 12 and so 16 + 14 + 12 = 42
sry i'm dumb
Sounds like sound logic to me :), do you know why you can do that though?
no
that's the reason i opened this
Cool, have you learnt about similar triangles?
yeah. a bit
Right, so you know how if the triangles have the same angles and triangle "A" has a side of size "8" and triangle "B" has a side of length "4", then all the rest of the sides of "B" would be half of the sides of "A"?
yea
Well, this is just the same thing, but the triangles are inside each other
So if the length of AD is 8 and AE is 16 then AE is twice AD, so AC would be twice AD + DF + FB :)
Because ADE and ABC are similar
ok so basically, I'll just consider ABC an enlarged version of ADE, and calculate the the values accordingly
yea I got it
tysm
Np :)
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2018^2018/20
Whats the remainder
ok first simplify 2018, whats 2018 (mod 20)?
What's a mod
wait are you not doing number theory?
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Can someone correct my answers please
i. 11/18/2020
ii.83.33
iii. I didn't know how to get it
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@stuck kayak Has your question been resolved?
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$\arctan\left(\frac{2x}{1-x^2}\right)+\operatorname{arccot}\left(\frac{\left(1-x^2\right)}{2x}\right)=\frac{\pi}{3}-1$
ƒ(Why am. I here)=I don't Know
ƒ(Why am. I here)=I don't Know
find $\alpha$
ƒ(Why am. I here)=I don't Know
so to start
hmm
$2\arctan\left(\frac{2x}{1-x^2}\right)=\frac{\pi}{3}-1$
ƒ(Why am. I here)=I don't Know
$\arctan\left(\frac{2x}{1-x^2}\right)=\frac{\pi}{6}-\frac{1}{2}$
ƒ(Why am. I here)=I don't Know
now let $x=tan(u)$
Just make sure to note the domain when you invert it
ƒ(Why am. I here)=I don't Know
so If I do this, I only solve in $(0, \frac{\pi}{2})$
right?
ƒ(Why am. I here)=I don't Know
or whatever the argument is
so $2u= \frac{\pi}{6}-\frac{1}{2}$?
ƒ(Why am. I here)=I don't Know
Yes
ƒ(Why am. I here)=I don't Know
so here,what do I do exactly
x=tan(u)?
$\arccot \frac{1}{x} = \pi + \arctan x$ for x < 0 I believe
jewels!
right
You should do that where you made the case to invert it
this has got to be some form of art dude
Yep
ƒ(Why am. I here)=I don't Know
Compile Error! Click the
reaction for more information.
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give me a minute
$2\arctan \left ( \frac{2x}{1 - x^2} \right ) + \pi = \frac{\pi}{3} + 1$
jewels!
thanks!
remember now that 2x/(1 - x^2) < 0
ƒ(Why am. I here)=I don't Know
so $\arctan\left(\frac{2x}{1-x^2}\right)=\frac{1}{2}-\frac{\pi}{3}$
ƒ(Why am. I here)=I don't Know
ƒ(Why am. I here)=I don't Know
wdym
you should have done that with the original one as well
would've helped massively 😛
I meant you just left it at this
ƒ(Why am. I here)=I don't Know

slow down
uh
so when you defined $x = \tan t$, with our domain consideration $\arctan \tan 2t \neq 2t$
jewels!
since $t \in \left ( -\frac{\pi}{2}, \frac{\pi}{2} \right )$
jewels!
it would open up as pi - 2t yes?
ƒ(Why am. I here)=I don't Know
so
this is the positive case or the negative case
negative, right?
I think pi - 2t isnt right either wait we need to figure this out properly
arc means inverse right ?
yes
alright
so 2t lies in the interval (-pi, 0) in that case
pi + 2t shifts it to (0, pi) but that still isn't in the invertible range for us
this is why I hate inverse trig
sorry
wdym by phase shifts
shifting the argumnet to get it in range?
ok
where did you even get the question tho
a past JEE paper
what kind of intervals ?
probably (-pi, -pi/2) and (-pi/2, pi)
staring from here, again
im sorry for switching up gears again but I think I know what's best
since the invertible range of arccot is (0, pi) it would be better to do it with arccot in mind
so just converting the arctan to arccot and substituting tan 2t will be enough
so
$\left(2\operatorname{arccot}\left(\frac{\left(1-x^2\right)}{2x}\right)\right)=\frac{\pi}{3}-1$
ƒ(Why am. I here)=I don't Know
$\left(\operatorname{arccot}\left(\frac{\left(1-x^2\right)}{2x}\right)\right)=\frac{\pi}{6}-\frac{1}{2}$
ƒ(Why am. I here)=I don't Know
now what
x = tan u
why do you have parenthesis around the arccot

also is this the negative or positive case
Negative
Right
So 2t=π/6 -1/2
But this isn't close to the form of the og question
wheres the -pi then
Why 4x?
jewels!
2arccot(cot(2t))
Got it
i'll take your leave now sorry
this has taken much more time than i initially thought it would
Thanks a lot for the help
@blazing coyote Has your question been resolved?
so $4x=7 \pi/3 -1$?
ƒ(Why am. I here)=I don't Know
this feels very sus
<@&286206848099549185>
#help-42 message OG problem
nvm, I'll try this tomorrow
.clos
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The question is sus too
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hi
how can i decompose this matrix into sum of symetric and antisymetric matrix
$\begin{pmatrix}1&0&0\1&0&-2\0&0&1\end{pmatrix}$
lets call the matrix A
Slowaq
we want A=B+C where B is symmetric and C is antisymmetric
yes
what happens if you transpose both sides
wdym by both sides?
A=B+C
(B+C)^T?
no that would have been a step actually before obtaining A^T=B^T+C^T
you know that B is symmetric and C is antisymmetric
yes that should help
give me a second
$\begin{pmatrix}1&0&0\1&0&-2\0&0&1\end{pmatrix}=\begin{pmatrix}1&0.5&0\0.5&0&-1\0&-1&1\end{pmatrix}+\begin{pmatrix}0&-0.5&0\0.5&0&-1\0&1&0\end{pmatrix}$
Slowaq
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yw
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with b
p is 12.18
12,18
i cant get visual of the triangle
also they use trapezium formula in ms should i jump
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Can someone help me with this
is this. a test?
are these the eassesments
they were fr annoying
just remember the probabilities always add to 1
This is a past paper
I've solved questions like this
But for this one they give almost no information
so for the not shortest its 3/5 because 2/5+3/5 is 5/5
there is no other way other than these two so the top parts need to add together to get the bottom part
@split meadow Has your question been resolved?
So to get not lost
I need to do 2/5 + 7/10?
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heyy so I have this fraction $\frac{(\frac{y^2-x^2}{y})}{y^2}$ and I want to simplfy it
Specific Joe
$\frac{(\frac{y^2-x^2}{y})}{y^2}$
Specific Joe
well, what have you tried?
I tried multiplying the whole fraction by $y^2$ to cancel out the $y^2$ at the denominator $(\frac{y^2-x^2}{y})*y^2$
Specific Joe
to be clear you have $\frac{(y^2 - x^2)(\frac 1 y)}{y^2}$
b
yes
do you know $\frac 1 {y^2} \cdot \frac 1 y$?
b
that's it yeah
Specific Joe
👍
I see
at which point you can split that into two fractions
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Geometry Question (formulas are provided aswell as calculator- this is district assesment prep)
heres what ive done so far
ive found the volume of the fertilizer required, which is 576
ive set up the equation of 576= (volume of cylinder)+(volume of cone)
im thinking of substituting 8 and 14 in but im not sure because i dont think im supposed to do that
Would love some help on this, and suggestions if i come across problems like this
so how would i do that
If you expand the equation you have for volume
you will have a h_1 and h_2 naturally
then use substitution
h_1 = 14-h_2
that will get you h_2
then sub that back in and you will have h_1
ya
this for h1 or h2
okayy
ya
I do think this question is a bit bad tho
bad question in my op
thats kinda wild
i wanna get into tutoring
at that point in maths where i should learn how to teach
joined this today for that
rearrange for h at this point
it will be squared
take the pos value
negative heights are booky
ahh its a quadratic equation
times by the whole thing by 16pih
then do you know the quadratic formula
true true
still gona ask i was trying to help a guy with a triangle problem and i assumed he knew what cos and sin was
i was wrong
yeah kinda his courses fault tho
i dont do america i have no idea what that means
8th grade
ahhh
yehh that would be 2nd year high school for me
scotland
ohh wait im silly
x=h
i tought the middle part
^
you can pull h out here
and divide by the other side
so i divide both sides by h
i thought i was written as 1/(3*16pih)
nah
oka oka
thats ok
so pull out h then divide by the thing h is multyping
wdym pull out h
h(16pi +16pi/3)=14
i think my curriculum wants me to cut my main arteries cause i never learned any of this
dam cuz
we never went over any of this, they just gave the formulas
fr
because you gotta find out the details of what these formula mean
yea
in uni atm its really nice its all derived from fundamental theoroms
VERY DIFFICULT i will say
but cool
i only know this cause its something ive studied online
i recommend 3blue 1 brown
im asking this question of the behalf of like 20 kids who dont know how to do this LOL
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Ok so I manipulated the result to PQ = PB*PC/(PB+PC)
By Ptolemy I got AP = PB+AC so (PQ)(AP) = (PB)(PC)
Just some things I found in case I need it:
By power of point, (BQ)(QC) = (AQ)(AP)
So I also rewrote the result as QP^2 = (BP)(PC) - (BQ)(QC)
I tried stewart's theorem on BPC because angle BPA and CPA are 60 degrees
and got (BC)(QP) = (BP)(QC)
tried to manipulate it with some of the earlier things but hasn't worked out
not sure how to isolate BP*PC
@hybrid flint Has your question been resolved?
<@&286206848099549185>
I think I'm close
Ok so I applied cosine law with bpq bcq and bcq and manipulated them
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is this solution correct
i found this somewhere and i attempted it in the same way
Yes
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i’m wondering how my teacher got 0.999 (:
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(do you have an idea of how to do these?)
ik it does but its wrong
how do you mean it's wrong?
As in the solution says that the vectors dont span R^2
To span $\mathbb{R}^2$ you need two linearly independent vectors
fwa
it does span R^2 no?
It does
It should
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How do i do this
recall that concavity is determined by the second derivative
yea
can you write down g''(x)?
you are given g'(x) so g''(x) is the derivative of g'(x)
using ftoc
g'' = e^-x^2
yes
is this function positive on (0, 2)?
I'll get to that
note that you can also eliminate E
eb d
the only way to get g'(x) = 0 is to set x=0, but x>0 hence no point of inflection
try estimating the integral, roughly
between 0 and 2
yes
but how do i do it mathematically
try plotting e^(-x^2)
you can't
ibp?
yeah
so on these kinds of problems do i just estimate?
but notice that as you do integral frol zero to x, and increase x, you "gain" more area hence the integral is always positive
in general if $f(x)$ is positive on some interval $(a, b)$ then $\int_{a}^{b} f(x) dx > 0$
artemetra
if the normal function?
sorta, you write what i wrote
I see
like say
f(x) = x^5 and intabf(x)
from 0 to inf since normal function is positive, would that also mean int ( 0 --> inf ) is also positive
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Stats and Probability, Least Squares Regression
how do I find the mass of the object at 27 minutes
plug 27 into your line
yeah like substitute it into the x right?
that's what it means to plug in
nvm I realized what I did wrong
mis type
thanks for the help
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$\int_{1}^{x^4} -\sin{(xt)}dt + \frac{4\cos{(x^5)}}{x}$
Jasmine<3
That's what I'm getting
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$x^3 + 12x^2 + 39x + 28$
Alex
RRT?
rational root theorem
Vitaes' formula
you'll get 3 equations in 3 variable from this, solve them to get the roots
Lmao what a troll
what do you mean, troll?
I dont understand that
It'll result in the same cubic
When you solve that system
You'll return to the same cubic eventually
yeah, but you'll get alpha, beta and gamma
Complete the cube, it is very easy tbh
I don't get what you mean, we'll arrive at the same cubic equation in Alpha or beta or gamma
When we attempt to solve the equation
We want to factorise it
so for that finding alpha, beta, gamma are sufficient
say we get alpha=1, beta=2, gamma=3
(x-1)(x-2)(x-3) will be the factorisation
My point is, to get those 3 roots you'll end with the same equation to solve
didn't realise, sorry
Go ahead and try to solve the system you make
It'll just lead to the original equation
Just this
I'd recommend noticing the coefficients and realising -1 just satisfies this thing since 39+1=40 and 12+28 also equals 40
Then dividing the whole thing by x+1
To get it into the form (x-1)(quadratic)
And factorise the quadratic
i know to complete the square but not the cube
isnt that using rrt?
rational root theorem
The rational root theorem in algebra states that a polynomial equation with integer coefficients can only have rational number
roots if the leading coefficient is divisible
by the denominator of the fraction.
I don't see how what I recommend uses that?
those questions in the cube square format are pretty common for rrt
I don't either, just saying what it is
Regardless, competing the cube won't be a problem either, break 28 into 27+1 and continue from there
think its a way of factorising using synthetic division
It is the same, u can realize the (x+a)^3, makes the x^2 coefficient = 12 when a = (find this)
Alex
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i'm stuck at B and C.
i've tried getting the 90th percentile to get the value in B, but i'm still not sure about my answer.
i thought, since above 10% of the distribution was required, getting the 90th percentile would be the right choice (since if i would get the 10th percentile, it would either be equal to 10% or less than 10%,)
same goes with C. i don't know what to apply since B and C sounds like they're looking for the same thing
@native hollow Has your question been resolved?
<@&286206848099549185>
@native hollow Has your question been resolved?
@native hollow Has your question been resolved?
Yes, so you need the score of the 50 * 9/10 = 45th student
There are 50 students overall so count backwards by 5, (50, 49) and (48, 47, 46)
So the category is actually 185-189
I'm not sure what the difference between B and C is
@native hollow Has your question been resolved?
ohhhhh i see
thanks a lot!
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I want to prove by induction that
$P(\bigcap_{i=1}^nA_i)=P(A_1)\cdot \prod_{k=2}^nP(A_k|\bigcap_{i=1}^{k-1}A_i)$
Bob Goldham
to do this
I did something like
first I show that it holds for n=1
then
assuming it holds for n, we can
$P(\bigcap_{i=1}^nA_i)=P(A_1)\cdot \prod_{k=2}^nP(A_k|\bigcap_{i=1}^{k-1}A_i)$
Bob Goldham
$\Leftrightarrow P(\bigcap_{i=1}^nA_i) + P(A_{n+1}) - P(A_{n+1} \cup \bigcap_{i=1}^nA_i) =P(A_1)\cdot \prod_{k=2}^nP(A_k|\bigcap_{i=1}^{k-1}A_i) + P(A_{n+1}) - P(A_{n+1} \cup \bigcap_{i=1}^nA_i)$
Bob Goldham
adding the same term to both sides
$\Leftrightarrow P(\bigcap_{i=1}^{n+1}A_i) =P(A_1)\cdot \prod_{k=2}^nP(A_k|\bigcap_{i=1}^{k-1}A_i) + P(A_{n+1}) - P(A_{n+1} \cup \bigcap_{i=1}^nA_i)$
Bob Goldham
LHS is just the intersection for n+1 since P(A intersect B)=P(A)+P(B)-P(A union B)
now what? How do I proceed from here?
that RHS looks a bit... messy
can't use the same trick as here, since that'd indirectly use the statement I'm trying to prove about conditional probabilities
I could also put it into a form like this, though I'm not sure it's helpful:
$\Leftrightarrow P(\bigcap_{i=1}^{n+1}A_i) = P(A_1)\cdot \prod_{k=2}^n
\frac{P(\bigcap_{i=1}^{k}A_i)}{P(\bigcap_{i=1}^{k-1}A_i)}
+ P(A_{n+1}) - P(A_{n+1} \cup \bigcap_{i=1}^nA_i)$
Bob Goldham
<@&286206848099549185>
@coarse minnow Has your question been resolved?
questions like these is what makes math interesting for me
like, I dont understand any of that stuff but I wanna know
it's probabilities
baye's theorem yields this, which is the same thing again? I'm out of ideas here
yeah, I recognise the P lmao
I could also do this, but resolving the fraction in the product requires me to assume the statement I'm trying to prove
@coarse minnow Has your question been resolved?
@coarse minnow Has your question been resolved?
@coarse minnow Has your question been resolved?
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thank u
sophiaaaa
but
how do i remove thr fraction
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is this correct so far?
If the derivative at any point DNE then the whole derivative DNE right?
non diff fn
wdym
the derivative at f(3) does not exist right?
And for the last question
@cerulean cradle
Look good?
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@buoyant mirage Has your question been resolved?
Period is the distance it takes for a trigonometric function repeats itself, i.e. complete one cycle
ehhh not really it's more the length of a cycle
that made sense
tysm
tysm
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How do i determine the area (green) ?
I understand that i'm supposed to make a integral with set boundaries where it goes from (0,0) to (a,0)
That might be right, i haven't touched polar coordinate integral yet however
How do i create a double integral equation to solve the area A?
I can't seem to understand why i would want a double integral for this. Isn't this just "area" meaning a single variable or a single integral
yes you can solve it using a single integral
In that case the bounds would be from (0,0) to (a,0)
im trying to figure it out im still not sure
$\int^a_0 \frac{x^2}{a^2} + \frac{y^2}{b^2} -1 <= $
However i have to somehow fit the second criteria that 0 <= y <= x
Is there any more info in the question?
"Determine the area A and the coordinates(ux,uy) to the center of gravity of the ellipse sector D if..."
Well my first job would be to find the area A
Which to me seems like i just want to integrate the given function?
oh woops i assumed it was the point on the curve of the ellipse
x = B is the point where the ellipse meets the line y = x
Can we make it c instead
Merineth
now im confused lol
i'm integrating wrt a?
Why would you split the area into a triangle and the rest?
Yeah I’m asking him
oh sorry
makes it easier to calculate imo
$R_2$ is just a triangle. $R_1$ is an integral
Obotron
if we rearrange ellipse equation into the form y = f(x) then $R_1 = \int_{c}^{a}f(x) dx$
Since i'm given restrictions and i want to maximize a given function, wouldn't i be able to use Lagrange?
Obotron
which function are we maximizing ?
We are maximizing the function for the ellipse and the restriction would be the 0 <= y <=x
So i take the gradient of both and make a function
$\nabla f = \lambda \nabla g$
Merineth
where f is the given function for the ellipse and g is the restriction
i thought we are finding the area under the ellipse where 0 <= y <= x
lagrange finds the maximum/minimum of a function
Equation of ellipse is: $\frac{x^2}{a^2}+\frac{y^2}{b^2} = 1$ which can be written as: $y = \frac{b}{a} \cdot \sqrt{a^2-x^2}.$
It kind of makes sense to divie it into two integrals and sum them up
since as you pointed out, one could just be a triangle
Obotron
yes i think its the easiest method
you can find point c by equating the equation of the ellipse equal to x
$\frac{b}{a} \cdot \sqrt{a^2-x^2} = x$
Obotron
@austere moth Has your question been resolved?
Ok here is a summary of my method:
- Write equation of ellipse is: $\frac{x^2}{a^2}+\frac{y^2}{b^2} = 1$ as: $y = \frac{b}{a} \cdot \sqrt{a^2-x^2}.$
Obotron
- split the area into 2 regions as such
- Calculate c by equating the ellipse equation to the line y = x: i.e $\frac{b}{a} \sqrt{a^2-c^2} = c$
Obotron
- Now R2 is just a simple triangle with height and width equal to c. $R_2 = 0.5c^2$
Obotron
- R1 is a fairly simple integral: $R_1 = \int_{c}^{a}f(x) dx$
Obotron
@austere moth im trying :(
@austere moth Has your question been resolved?
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Yo
Any idea here
Btw it | Un - 2 | its just a mistake
Um
<@&286206848099549185> AAAAH
......
Help pls this ez but idk how:
I can give more details its just because that all it needs
What is the questiom
