6x^4+7x^3y+5x^2y^2-xy^3-2y^4=6x^4+7x^3y+2x^2y^2+3x^2y^2-xy^3-2y^4=x^2(6x^2+7xy+2y^2)+y^2(3x^2-xy-2y^2)=x^2(2x+y)(3x+2y)+y^2(x-y)(3x+2y)=(3x+2y)[x^2(2x+y)-y^2(x-y)].