化简(3x^3-x^2y) / (3x^3+2x^2y-xy^2) = ( ) / (x+y)
(3x^3-x^2y) / (3x^3+2x^2y-xy^2)
=(3x-y)x^2/[x(3x^2+2xy-y^2)]
=(3x-y)x^2/[x(3x-y)(x+y)]
=x/(x+y)