问答题
ydx-（x+y3）dy=0
问答题ydx-（x+y3）dy=0
ydx-xdy=（x2+y2）dx
问答题ydx-xdy=（x2+y2）dx
2xydx+（x2+1）dy=0
问答题2xydx+（x2+1）dy=0
