z=f(x+y,x)有连续的二阶偏导数,则a^2z/ay^2=多少?

Question

z=f(x+y,x)有连续的二阶偏导数,则a^2z/ay^2=多少?

Answer 1

∂z/∂y=f1(x+y,x)*∂(x+y)/∂y+f2(x+y,x)*∂(x)/∂y=f1(x+y,x)
∂²z/∂y²=∂f1(x+y,x)/∂y=f11(x+y,x)