一、（1）(1/a+1/b)²÷(1/a²-1/b²)；（2) (x/x+y+2y/x+y）·xy/x+2y÷（1/x+1/y）；(3) (a+b/a-b)²·2a-2b/3a+3b-a²/a²-b²÷a/b；

、=(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)

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) 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)

(1)原式=（b+a）^2/a^2*b^2 *(a^2*b^2)/(b+a)(b-a)
=(b+a)/(b-a)
(2)原式=(x+2y/x+2y)*xy/x+2yx+2y^2
=x^2y+2y^2/x^2+2xy^2/x+2yx+2y^2
= ..........

甲乙两车从A,B两地相向而行,经过4小时，甲车行驶了全程的70%

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