Hi,
"if u=f(x,y) is a differentiable function with x=e^s((cos(t)) y=e^s((sin(t)) show that show d2u/dx2+d2u/dy2 = e^(-2s)[d2u/ds2+ d2u/dt2
I know how to find dx/dt dy/ds etc, but I don't know how to find anything involving u because it is only defined as f(x,y).
Thank your for your help.