anonymous
  • anonymous
Integrals and linear algebra?
Mathematics
  • Stacey Warren - Expert brainly.com
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SOLVED
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schrodinger
  • schrodinger
I got my questions answered at brainly.com in under 10 minutes. Go to brainly.com now for free help!
anonymous
  • anonymous
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anonymous
  • anonymous
I can't figure out the damn matrix lol.
anonymous
  • anonymous
Please help.

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tkhunny
  • tkhunny
Are we missing part (a)?
anonymous
  • anonymous
Okay, I guess I should include that.
anonymous
  • anonymous
i think it is just \([\frac{8}{3},2,2]\)
anonymous
  • anonymous
i think so too. It's 5 marks though. Is it really that easy?
anonymous
  • anonymous
because if you multiply that by \([a,b,c]\) written of course as a column, you get just what you want
anonymous
  • anonymous
Here is part a. I don't think it's required though.
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anonymous
  • anonymous
Hmm, Feels too easy lol.
anonymous
  • anonymous
Thanks!
anonymous
  • anonymous
it does seem easy, but i am fairly sure it works right?
anonymous
  • anonymous
Yeah it does.
anonymous
  • anonymous
ok
anonymous
  • anonymous
Can you answer another question similar to that?
anonymous
  • anonymous
i dunno my linear algebra is sometime weak, but i can try
anonymous
  • anonymous
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anonymous
  • anonymous
@tkhunny
anonymous
  • anonymous
So f(0)=c f(1)=a+b+c f(2)=4a+2b+c
anonymous
  • anonymous
so: |dw:1359170790953:dw|
anonymous
  • anonymous
right?
anonymous
  • anonymous
How did you deduce that matrix?
anonymous
  • anonymous
i am a bit confused because those are \(f\) values not \(p\) values. \(f(0)=0 f(1)=? , f(2)=?\) are you supposed to use \(p\) instead of \(f\) ?
anonymous
  • anonymous
But we are given: |dw:1359171043668:dw|
anonymous
  • anonymous
So yeah, How did you deduce that? @tkhunny
anonymous
  • anonymous
then i guess it is the same as the other one, because the integral is \(\frac{8}{3}a+2b+2\)
anonymous
  • anonymous
oops i meant \(\frac{8}{3}a+2b+2c\)
tkhunny
  • tkhunny
Never mind that silly thing, I still haven't figured out what we're doing, here. I believe the premise is that we CANNOT find an antiderivative of f(x), but we CAN find one for p(x).
anonymous
  • anonymous
Yeah, I guess because f(x) isn't given.
anonymous
  • anonymous
Any ideas?
tkhunny
  • tkhunny
\(\int\limits_{0}^{2}p(x)\;dx = \int\limits_{0}^{2}ax^{2} + bx + c\;dx = \dfrac{8}{3}a + 2b + 2c \approx \int\limits_{0}^{2}f(x)\;dx\) I'm not sure what else we are looking at, here.
anonymous
  • anonymous
Well I posted the question. It dosen't make sense to me though :( .
anonymous
  • anonymous
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tkhunny
  • tkhunny
I see it. Sorry, it took me a minute. It will take a moment to code and it requires Part A!
tkhunny
  • tkhunny
Part A \[A = \left[\begin{matrix}0 & 0 & 1 \\ 0 & 1 & 1 \\ 4 & 2 & 1\end{matrix}\right]\] \[\left(\begin{matrix}f(0) \\ f(1) \\ f(2)\end{matrix}\right) = A * \left(\begin{matrix}a \\ b \\ c\end{matrix}\right)\] \[A^{-1} = \dfrac{1}{4}\left[\begin{matrix}1 & -2 & 1 \\ -4 & 4 & 0 \\ 4 & 0 & 0\end{matrix}\right]\] \[A^{-1\cdot}\left(\begin{matrix}f(0) \\ f(1) \\ f(2)\end{matrix}\right) = \left(\begin{matrix}a \\ b \\ c\end{matrix}\right)\]
tkhunny
  • tkhunny
Part B \[i = \left(\begin{matrix}\dfrac{8}{3} & 2 & 2\end{matrix}\right)\cdot \left(\begin{matrix}a \\ b \\ c\end{matrix}\right)\]
tkhunny
  • tkhunny
@Dido525 Are you SURE you don't want to do the glorious Part C? It's now staring at you!
anonymous
  • anonymous
Sorry I was eating lol.
anonymous
  • anonymous
Well I will attempt it.
anonymous
  • anonymous
Well We know: |dw:1359173248519:dw|
anonymous
  • anonymous
right?
anonymous
  • anonymous
@tkhunny
tkhunny
  • tkhunny
No, \(A\) is no longer useful. Look at the very bottom of Part A and compare that carefully to Part B, right below it. Make the substitution and you are done. \(C = B\cdot A^{-1}\) I guess I forgot to say : \[B = \left(\begin{matrix}\dfrac{8}{3} & 2 & 2\end{matrix}\right)\]
anonymous
  • anonymous
So it would be: |dw:1359174107470:dw|
anonymous
  • anonymous
Like the inverse of A.
anonymous
  • anonymous
Which I have to find.
tkhunny
  • tkhunny
No, that's \(B\cdot A\) you need \(B\cdot A^{-1}\).
anonymous
  • anonymous
yeah. I mean Once I find the inverse I set it up like that right?
tkhunny
  • tkhunny
Yes, but for future reference, don't write \(A\) as a place holder for \(A^{-1}\). Very confusing.
anonymous
  • anonymous
Alright. Lets grind this out...
tkhunny
  • tkhunny
You may find the result surprising. It's a bit, shall we say, regular!
anonymous
  • anonymous
2/3 2/3 2/3 ?
anonymous
  • anonymous
for c?
tkhunny
  • tkhunny
Big C, not little c, but yes. Are you surprised?
anonymous
  • anonymous
I am actually! :P .
anonymous
  • anonymous
Can I ask something?
anonymous
  • anonymous
How did you make that substitution?
tkhunny
  • tkhunny
What a strange result. Sample the function at both ends and in the middle and then use 2/3 of those values and you've created a quadratic approximation. Too simple!
tkhunny
  • tkhunny
You have to come to terms with the very last equation in my Part A. This gives you an expression for (a b c )^T in terms of f(0), f(1), and f(2). We are simply substituting this expression for (a b c)^T from Part B.
anonymous
  • anonymous
And shoudn't the second row of matrix a say 1 1 1 ? Instead of 0 1 1.
anonymous
  • anonymous
Matrix A*
tkhunny
  • tkhunny
Whoops! You are right. This changes things and that silly 2/3 things IS as weird as it looked. I like \(\left(\begin{matrix}\dfrac{1}{3} & \dfrac{4}{3} & \dfrac{1}{3}\end{matrix}\right)\) much better.
tkhunny
  • tkhunny
You should get \(A^{-1} = \dfrac{1}{2}\left[\begin{matrix}1 & -2 & 1 \\ -3 & 4 & -1 \\ 2 & 0 & 0\end{matrix}\right]\) Important lesson, never mess up Matrix \(A\) when you will need it later!
anonymous
  • anonymous
Yep Yep, I did XD .
anonymous
  • anonymous
Except I didn't bother factoring out 1/2 .
tkhunny
  • tkhunny
Perfect. The factoring just makes it simpler to write.
anonymous
  • anonymous
Still lost on the substitution... Or else I got you just fine.
tkhunny
  • tkhunny
Just calculate \(B\cdot A^{-1}\)
anonymous
  • anonymous
I did. I got it correct and everything. I just don't get why that works.
anonymous
  • anonymous
OOO!!!! I see it! Nvm.
anonymous
  • anonymous
Thanks so much!!!
tkhunny
  • tkhunny
Hmmm...\(\left(\begin{matrix}a \\ b \\ c\end{matrix}\right)\) is the key. Stare at it until it soaks in. That's all I did while you were having dinner. :-)
anonymous
  • anonymous
Yep, you just substituted for that right?
tkhunny
  • tkhunny
That's it, but I used Part A to develop the substitution. Do we remember someone saying Part A was not helpful? Good work! Way to hang in there.
anonymous
  • anonymous
Thank you so much! You helped me out immensely :) .

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