z=x^y=x^f(x) lnz=f(x)*lnxz'/z=f'(x)*lnx+f(x)/x z'=[f'(x)*lnx+f(x)/x]*z=(x^y)*[f'(x)*lnx+f(x)/x]
dz/dx=∂z/∂x+∂z/∂y·∂y/∂x=yx^(y-1)+x^yy'(x)lnx
