求偏导数： (1).z=e^(xy) ∂z/∂x=ye^(xy)；∂z/∂y=xe^(xy). (2).z=ln[y+√(x²+y²)] ∂z/∂x=[x/√(x²+y²)]/[y+√(x²+y²)]=x/[x²+y²+y√(x²+y²)] ∂z/∂y=[1+y/√(x²+y²)]/[y+√(x²+y²)]=[y+√(x²+y²)]/[x²+y²+y√(x²+y²)].
