由题知,
z=f(xy,y)
所以,
dz/dx=f1(xy,y)*y
而
d²z/dxdy
=d(dz/dx)/dy
=d(f1(xy,y)*y)/dy
=f1(xy,y)+y[f11(xy,y)*x+f12(xy,y)]
=f1+xy*f11+y*f12
其中,f(u,v)对u求导记做f1,对y求导记做f2