求函数z=(x+y)sin(x-y)的偏导数∂z/∂x,∂z/∂y
问题描述：
求函数z=(x+y)sin(x-y)的偏导数∂z/∂x,∂z/∂y
答
∂z/∂x只对x求导数,而把y看作一个常数,∂z/∂x=(x+y)'sin(x-y)+(x+y)sin(x-y)'=
sin(x-y)+(x+y)cos(x-y)
∂z/∂y只对y求导数,而把x看作一个常数,∂z/∂y=(x+y)'sin(x-y)+(x+y)sin(x-y)'
=sin(x-y)+(x+y)[-cos(x-y)]
=sin(x-y)-(x+y)cos(x-y)