已知A=x^2+xy+y^2,B=-2xy-x^2,则3A-4B=
问题描述:
已知A=x^2+xy+y^2,B=-2xy-x^2,则3A-4B=
答
3A-4B=3﹙x²+xy+y²﹚-4﹙﹣2xy-x²﹚
=3x²+3xy+3y²+8xy+4x²
=7x²+11xy+3y².