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

3x-2y-5xy-(2x-3y+2xy)
=3x-2y-5xy-2x+3y-2xy
=x+y-7xy
=4-7×(-7)
=4+49
=53