计算(x-2y-1)(x-2y+1)-(x-2y-1)²
问题描述：
计算(x-2y-1)(x-2y+1)-(x-2y-1)²
答
(x-2y-1)(x-2y+1)-(x-2y-1)²
=[(x-2y)-1][(x-2y)+1)]-[(x-2y)-1]²
=(x-2y)²-1-(x-2y)²+2(x-2y)-1
=2(x-2y)-2
=2x-4y-2