先化简,再求值:3x-2y-5xy-(2x-3y+2xy),其中x+y=4,xy=-7
问题描述:
先化简,再求值:3x-2y-5xy-(2x-3y+2xy),其中x+y=4,xy=-7
急
答
3x-2y-5xy-(2x-3y+2xy)
=3x-2y-5xy-2x+3y-2xy
=x+y-7xy
=4-7×(-7)
=4+49
=53