解
(2x²-2ax-y)-2(bx²-3x+2y-1)
=2x²-2ax-y-2bx²+6x-4y+2
=(2-2b)x²+(6-2a)x-5y+2
与x取值无关
∴
2-2b=0
6-2a=0
∴b=1,a=3
∴(a-b)-(a+b)
=a-b-a-b
=-2b
=-2×1
=-2