y^2 で割って
-(1/y)'+(2/x)*(1/y)=x^2
u=1/y とおく
-u'+(2/x)u=x^2
-u'/x^2+(2/x^3)u=1
-(u/x^2)'=1
u/x^2=-x+C
y=1/(Cx^2-x^3)