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### Messages - Xiaozeng Yu

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##### MidTerm / Re: MT, P1
« on: October 11, 2013, 10:05:54 AM »
thank u prof.

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##### MidTerm / Re: MT, P1
« on: October 10, 2013, 10:51:42 PM »
t is defined everywhere...

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##### MAT244 Misc / Re: Homework Questions
« on: October 10, 2013, 10:14:20 AM »
office hour...

4
##### MidTerm / Re: MT, P1
« on: October 10, 2013, 09:53:07 AM »
And where this solution is defined? $\DeclareMathOperator{\arctanh}{arctanh}$

BTW, when collecting MT I have seen this problem and in many papers integration was atrocious.

As long as $|y|<1$ we have $\int \frac{dy}{1-y^2}=\arctanh (y)$ (inverse hyperbolic function $\tanh$) and then
$y=\tanh (t)=\frac{{e^t}-e^{-t}}{e^{t}+e^{-t}}$ (similar to $\int \frac{dy}{1+y^2}=\arctan(y)$).

hmm...yea...-1<y<1  T.T i feel i'm screwed...

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##### MidTerm / Re: MT, P4
« on: October 10, 2013, 09:43:00 AM »
ahh...omg, because the rectangle must contain the initial value point (0,1) in order to have an unique solution of the initial value problem. sin1>0 make the function increasing, so the retangle (a<0<b, 0<y<pi) which containing the initial point contains the unique solution function of (0,1) which is increasing?

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##### MidTerm / Re: MT, P2
« on: October 10, 2013, 09:27:59 AM »
Xuewen Yang,

good job, for multiplication do not use * (it is a convolution, different operation) use either \cdot like in $a\cdot b$ or \times like $a\times b$.

Xiaozeng Yu, no point to post inferior solution (scan) after superior (typed) has been posted. This time I awarded "scan posted after scan", but not in the future.

sorry, it took me a while figuring out how to post the non-oversized version of my work...

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##### MidTerm / Re: MT, P1
« on: October 09, 2013, 10:52:39 PM »
For Xiaozeng Yu,

Is there a problem with the sign change? from "plus" (2nd row) to "minus" (3rd row) ?

no mistake. $d(\ln(1-y))/dt = -1/(1-y)$.

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##### MidTerm / Re: MT, P6
« on: October 09, 2013, 10:45:20 PM »
6 Y just not equal to 0, not y>0, typo

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##### MidTerm / Re: MT, P6
« on: October 09, 2013, 10:40:30 PM »
6

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##### MidTerm / Re: MT, P5
« on: October 09, 2013, 10:40:12 PM »
5

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##### MidTerm / Re: MT, P4
« on: October 09, 2013, 10:39:57 PM »
4

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##### MidTerm / Re: Mt, P3
« on: October 09, 2013, 10:39:42 PM »
3

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##### MidTerm / Re: MT, P2
« on: October 09, 2013, 10:39:24 PM »
2

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##### MidTerm / Re: MT, P1
« on: October 09, 2013, 10:18:28 PM »
1

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##### MAT244 Misc / duration of quiz1
« on: September 27, 2013, 04:20:32 PM »
how long does the quiz take, 30min?

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