Question

（2014•海沧区模拟）计算：（[1/a−1]-[1/a+1]）÷2=[1a2−1

Answer 1

原式=[

a+1

(a+1)(a−1)-

a−1

(a+1)(a−1)]×

1/2]=[2

a2−1×

1/2]=

1

a2−1．

故答案为：

1

a2−1