∂z/∂x只對x求導數,而把y看作一個常數,∂z/∂x=(x+y)'sin(x-y)+(x+y)sin(x-y)'=
sin(x-y)+(x+y)cos(x-y)
∂z/∂y只對y求導數,而把x看作一個常數,∂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)