已知2x-y=5,求多项式-3(2x-y)^2+3(2x-y)-1/2(2x-y)+2(2x-y)^2的值

问题描述:

已知2x-y=5,求多项式-3(2x-y)^2+3(2x-y)-1/2(2x-y)+2(2x-y)^2的值

解由2x-y=5
即-3(2x-y)^2+3(2x-y)-1/2(2x-y)+2(2x-y)^2
=-3(2x-y)^2+2(2x-y)^2+3(2x-y)-1/2(2x-y)
=-(2x-y)^2+(5/2)(2x-y)
=-5²+(5/2)×5
=-25+25/2
=-25/2