求由方程cos（xy）=x^2*y^2 所确定的y的微分
问题描述：
求由方程cos（xy）=x^2*y^2 所确定的y的微分
答
-sin(xy)[ydx+xdy]=2xy^2*dx+x^2*2ydy-sin(xy)ydx-sin(xy)xdy=2xy^2*dx+2x^2*ydy-2x^2*ydy-sin(xy)xdy=2xy^2*dx+sin(xy)ydx-[2x^2*y+sin(xy)x]dy=[2xy^2+sin(xy)y]dxdy/dx=-[2xy^2+sin(xy)y]/[2x^2*y+sin(xy)x]