1、=(1/a+1/b)²/(1/a+1/b)(1/a-1/b)
=(1/a+1/b)/(1/a-1/b)
=(b+a)/(b-a) 分子分母同时乘以ab
2、=(x+2y)/(x+y) ×xy/(x+2y) ÷(x+y)/xy
=xy/(x+y)×(x+y)/xy
=1
3、=(a+b)²/(a-b)² ×2(a-b)/3(a+b) -a²/(a+b)(a-b)×b/a
=2(a+b)/3(a-b) -ab/(a+b)(a-b) 这个题目感觉有点不完整�԰� (a+b/a-b)²��2a-2b/3a+3b-a²/a²-b²��a/b��һ���ڸ�һ�İɣ������ġ���һ������ȷ��