x平方+xy-2y平方+2x+7y-3因式分解怎么做,谢谢

x平方+xy-2y平方+2x+7y-3=(x-y)(x+2y)+2x+7y-3用待定系数法(x-y+m)(x+2y+n)=(x-y)(x+2y)+n(x-y)+m(x+2y)+mn=(x-y)(x+2y)+nx-ny+mx+2my+mn=(x-y)(x+2y)+x(n+m)+y(2m-n)+mnm+n=22m-n=7mn=-33m=9m=3n=-1所以(x-y+m)(x+2...