Question

计算

4a

a2-1

+

1+a

1-a

-

1-a

1+a

的结果是______．

Answer 1

原式=

4a

(a+1)(a-1)

+

-(a+1)2

(a+1)(a-1)

+

(a-1)2

(a+1)(a-1)

=

4a-(a+1)2+(a-1)2

(a+1)(a-1)

=

0

(a+1)(a-1)

=0．
故答案为0．