设x+y=5,xy=负3,求(2x-3y-2xy)-(x-4y+xy)的值
问题描述:
设x+y=5,xy=负3,求(2x-3y-2xy)-(x-4y+xy)的值
答
(2x-3y-2xy)-(x-4y+xy)
=2x-3y-2xy-x+4y-xy
=(2-1)x+(-3+4)y+(-2-1)xy
=x+y-3xy
因为x+y=5,xy=-3
所以原式=5+9=14