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Possible Duplicate:
How does partial derivative work?

If $\frac{\partial u}{\partial s}$ is equal to $$e^s \cos(t) \frac{\partial u}{\partial x} + e^s \sin(t) \frac{\partial u}{\partial y},$$ what $\frac{\partial^2 u}{\partial d s^2}$ is equal to?

What expression are we suppose to get? I have been trying to figure out what to do for a hour, but I am quite lost. Doesn't the second partial derivative of $s$, give the same thing?

Any help would be appreciated. Thanks.

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    $\partial ds^2$ looks like a typo. There shouldn't be both a $\partial$ and a $d$.2012-11-11
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    That depends. Do $x$ and $y$ depend on $s$?2012-11-11
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    Probably you should say what variables are functions of what other variables. Partial derivatives depend on that information.2012-11-11

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