当x+y=-3,求(2x2+xy+3y2)-(x2-xy+2y2)的值,速求!
问题描述:
当x+y=-3,求(2x2+xy+3y2)-(x2-xy+2y2)的值,速求!
答
(2x2+xy+3y2)-(x2-xy+2y2)
=2x²+xy+3y²-x²+xy-2y²
=x²+2xy+y²
=(x+y)²
=(-3)²
=9