求x^2+xy-y^2和2x^2+xy+3y^的和

问题描述:

求x^2+xy-y^2和2x^2+xy+3y^的和

(x^2+xy-y^2)+(2x^2+xy+3y^2)
=x^2+xy-y^2+2x^2+xy+3y^2
=(1+2)*x^2+(1+1)*xy+(-1+3)*y^2
=3x^2+2xy+2y^2