当2x-y=5时,求-(2x-y)的二次方+3(2x-y)-二分之一(2x-y)+3(2x-y)的二次方的值.

因为 2x - y = 5
-(2x-y)^2 + 3(2x-y) - (1/2)(2x-y) + 3(2x-y)^2
= 2(2x - y)^2 + (5/2)(2x-y)
= 2×5^2 + (5/2)×5
= 50 + 25/2
= 125/2
= 62又(1/2)