解：用链式法则即可：∂u/∂x=e^y∂u/∂y=x(e^y)∂z/∂x=f1·(∂u/∂x)+f2=f1·e^y+f2∂²z/∂x∂y=e^y·[f11·∂u/∂y+f13]+f21·∂u/∂y+f23=e^y·[f11x(e^y)+f13]+f21·x(e^y)+f23=[x(e^2y)]f11+(e^y)f13+[x(e^y)]f21+f23
