e1设n=F(,y,z,xz=/f(,p,y=9(x)求如 dx Solution z du_aF,af dy aF(aafdy dx Ox ay dx az(ax ay dx =Fi+ F2o+F3f+ F352 K心1. ( , , ), ( , ), ( ), . dx du ex 设u = F x y z z = f x y y =  x 求 Solution. u xyz xyx x     +    +  +  = dx dy yf xf zF dx dy yF xF dx du =  +  +   +   1 2 3 1 3 2 F F F f F f