先化简,后求值:(1+1/x−2)÷x2−2x+1x2−4,其中x=-5.

问题描述:

先化简,后求值:(1+

1
x−2
x2−2x+1
x2−4
,其中x=-5.

(1+

1
x−2
x2−2x+1
x2−4

=
x−2+1
x−2
÷
(x−1)2
(x+2)(x−2)
(3分)
=
x−1
x−2
×
(x+2)(x−2)
(x−1)2
(4分)
=
x+2
x−1
,(5分)
当x=-5时,原式=
x+2
x−1
=
−5+2
−5−1
1
2
.(7分)