Question

计算，要写过程

(a+b)²-4ab=
（x-y）²-4（x-y-1）=
（a+b）²-4ab=

Answer 1

解
(a+b)²-4ab
=(a²+2ab+b²)-4ab
=(a²-2ab+b²)
=(a-b)²

(x-y)²-4(x-y-1)
=(x-y)²-4(x-y)+4
=[(x-y)-2]²
=(x-y-2)²

Answer 2

解：(a+b)²-4ab=﹙a－b﹚²;
（x-y）²-4（x-y-1）=﹙x－y－2﹚²;
（a+b）²-4ab=﹙a－b﹚²﹙a＋b﹚².