题目内容
先化简再求值:(
-
)÷(a-2),其中a是方程x2-x-1=0的根.
3a |
a2-1 |
a |
a-1 |
原式=[
-
]•
=
•
=-
=-
,
∵a是方程x2-x-1=0的根,
∴a2-a-1=0,即a2-1=a,
则原式=-
=-1.
3a |
(a+1)(a-1) |
a(a+1) |
(a+1)(a-1) |
1 |
a-2 |
=
-a(a-2) |
(a+1)(a-1) |
1 |
a-2 |
=-
a |
(a+1)(a-1) |
=-
a |
a2-1 |
∵a是方程x2-x-1=0的根,
∴a2-a-1=0,即a2-1=a,
则原式=-
a |
a |
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