(-3xy-7y)+[4x-3(xy+y-2x)],其中xy=-2,x-y=3,先化简,再求值._数学解答

(-3xy-7y)+[4x-3(xy+y-2x)],其中xy=-2,x-y=3,先化简,再求值.

人气：343 ℃　时间：2019-08-21 15:28:07

解答

(-3xy-7y)+[4x-3(xy+y-2x)],
=-3xy-7y+4x-3xy-3y+6x
=-6xy+10x-10y
=-6xy+10(x-y) xy=-2,x-y=3
=-6×(-2)+10×3
=18+30
=48