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
,其中x=-5.
x2−2x+1
x2−4
答
(1+
)÷1 x−2
x2−2x+1
x2−4
=
÷x−2+1 x−2
(3分)(x−1)2
(x+2)(x−2)
=
×x−1 x−2
(4分)(x+2)(x−2) (x−1)2
=
,(5分)x+2 x−1
当x=-5时,原式=
=x+2 x−1
=−5+2 −5−1
.(7分)1 2