Z‘x=(-y^2/x^2)/(1+y^2/x^2)=-y^2/(x^2+y^2)
Z‘y=arctan(y/x)+xy/(x^2+y^2)
dz=[-y^2/(x^2+y^2)]dx+[arctan(y/x)+xy/(x^2+y^2)]dy
求z=yarctan(y/x)的全微分,dz/dx,dz/du
Z‘x=(-y^2/x^2)/(1+y^2/x^2)=-y^2/(x^2+y^2)
Z‘y=arctan(y/x)+xy/(x^2+y^2)
dz=[-y^2/(x^2+y^2)]dx+[arctan(y/x)+xy/(x^2+y^2)]dy