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### Topics - Emily Deibert

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16
##### Textbook errors / Broken link in web bonus problem week 4 #6
« on: October 08, 2015, 03:37:58 PM »

17
##### Textbook errors / Typo in HA3 P3?
« on: October 03, 2015, 05:54:34 PM »
I asked this in the board for HA3 P3 as well but I am cross-posting here.

Quote
Just wondering, is there a typo in the original problem? The equation given is:
Au_{tt} + 2Bu_{tx} + Cu_{tt}
But I think the last term should be with respect to x:
Au_{tt} + 2Bu_{tx} + Cu_{xx}

Indeed, corrected

18
##### Quiz 1 / Quiz 1 - P3
« on: October 02, 2015, 12:35:31 AM »
This problem was: \begin{cases}
u_x + 3u_y = xy \\
u|_{x=0} = 0
\end{cases}

And my solution is:
\frac{dx}{1} = \frac{dy}{3} = \frac{du}{xy}

3dx = dy

3x - y = C

du=xydx

du = x(3x-C)dx

du = (3x^2-Cx)dx

u = x^3 - \frac{C}{2}x^2 + \phi(3x-y)

u = x^3 - \frac{3x-y}{2}x^2 + \phi(3x-y)

With initial condition, we have:

u|_{x=0}=\phi(-y)=0

So: $$\phi = 0$$

So the final solution will be:
u = x^3 - \frac{3x-y}{2}x^2

19
##### Textbook errors / Error in HA 2 Problem 1?
« on: October 01, 2015, 01:22:09 PM »
Hi Professor,

HA2 Problem 1 a) has as the fifth problem,
u_x + x^3u_x = 0

Did you perhaps mean
u_t + x^3u_x = 0

to make an equation involving partial derivatives with respect to t AND x, like the other problems?

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