Question

（2014•太仓市二模）先化简，再求值：[a−1/a÷(a−2a−1a)

Answer 1

原式=[a−1/a]÷

a2−2a+1

a

=[a−1/a]÷

(a−1)2

a

=[a−1/a]•[a

(a−1)2

=

1/a−1]，

当a=

2时，原式=

1

2−1=

2+1．