分组得：xy^2dx-xdx+yx^2dy-ydy=0或：(2xy^2dx+2yx^2dy)-2xdx-2ydy=0即：d(x^2y^2)-d(x^2)-d(y^2)=0通解为：x^2y^2-x^2-y^2=C或:：(x^2-1)(y^2-1)=C
