Question

已知0＜x＜1，则

(x- 1 x )2+4

-

(x+ 1 x )2-4

=（　　）

A． 2 x

B．2x

C．- 2 x

D．-2x

Answer 1

∵0＜x＜1，
∴原式=

[x2+( 1 x )2+2]

+

[x2+( 1 x )2-2]

=

(x+ 1 x )2

-

(x- 1 x )2

=x+

1

x

-（

1

x

-x）
=2x．
故选B．