# Homework Help: Partial derivative chain rule proof

1. Nov 11, 2012

### platinumrice

1. The problem statement, all variables and given/known data

If u=f(x,y) where x=escost and y=essint

show that d2u/dx2+d2u/dy2 = e-2s[d2u/ds2+d2u/dt2

2. Relevant equations

http://s11.postimage.org/sjwt1wkvl/Untitled.jpg

3. The attempt at a solution

ok i don't understand how they got to that

i don't know what d/ds is supposed to do exactly, i thought it was the second partial derivative of s, but it seems that it's not if we check the answer.

i basically got e^s cost (d^2/dx^2) + e^s sint (d^2u/dy^2), but they got 6 terms. i am kinda lost, can you explain to me what d/ds is supposed to do?

2. Nov 11, 2012

### Arkuski

Maybe you should try typing the problem a little clearer. I think I could help you with this.

3. Nov 11, 2012

### platinumrice

http://s10.postimage.org/fksqxnn3r/image.jpg

i got 6 terms, but the results are not the same for some reason and i am stuck. it has been like 2 hours and it has been really frustrating