先化简,再求值: 2x2+(-x2-2xy+2y2)-3(x2-xy+2y2),其中x=2,y=-1/2.
问题描述:
先化简,再求值:
2x2+(-x2-2xy+2y2)-3(x2-xy+2y2),其中x=2,y=-
. 1 2
答
2x2+(-x2-2xy+2y2)-3(x2-xy+2y2)
=-2x2+xy-4y2
当x=2,y=-
时,原式=-10.1 2