先化简再求值
问题描述：
先化简再求值
(-2xy+2x+3y)-(3xy+2x-2y)-(x+4y-xy),其中x、y满足x-y=10,xy=-4
答
(-2xy+2x+3y)-(3xy+2x-2y)-(x+4y-xy)
=-2xy+2x+3y-3xy-2x+2y-x-4y+xy
=-4xy-x+y
=-4xy-(x-y)
=-4×(-4)-10
=6