dx/dy=x/y-3x^3y
x/y=u dx=ydu+udy
3x^3y=3uy^4
ydu/dy+u=u-3uy^4
ydu/dy=-3uy^4
du/dy=-3uy^3
du/u=-3y^3dy
lnu=(-3/4)y^4+C0
ln(x/y)=(-3/4)y^4+C0(x-3x^3*y^2)意思是x减3乘以x的立方再乘以y的平方问题我自己已解决了，谢谢你的回答