what does d/ds (e^s cos(t)du/dx + e^s sin(t)du/dy) give, given that u = f(x,y)
i don't know how to manipulate d/ds and how to derive using d/ds. i am trying to simplify the expression, but i don't know, i just get stuck in the middle of can't get farther than here...
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
Homework Statement
If u=f(x,y) where x=escost and y=essint
show that d2u/dx2+d2u/dy2 = e-2s[d2u/ds2+d2u/dt2
Homework Equations
http://s11.postimage.org/sjwt1wkvl/Untitled.jpg
The Attempt at a Solution
ok i don't understand how they got to that
i don't know what d/ds is...