题目是否是φ(xy)??z/?x=-y^2/(3x^2)+yφ'(xy)?z/?y=2y/(3x)+xφ'(xy)x^2?z/?x-xy?z/?y+y^2=-y^2/3+x^2yφ'(xy)-2y^2/3-x^2yφ'(xy)+y^2=-y^2/3-2y^2/3+y^2=0
