z=e^(xy)sin(x+y)
az/ax= sin(x+y)a/ax {e^xy) + e^xy a/ax { sin(x+y) }
= y.e^(xy) sin(x+y) + cos(x+y) e^(xy)可不可以说清楚为什么az/ax= sin(x+y)a/ax {e^xy) + e^xy a/ax { sin(x+y) }会变成加号(uv)' = udv + vdu ( product rule )