题目内容
已知x+
=
,则x-
的值为( )
1 |
x |
7 |
1 |
x |
A.
| B.±2 | C.±
| D.
|
∵x+
=
,
∴(x+
)2=7
∴x2+
=5
(x-
)2=x2+
-2=5-2=3,
x-
=±
.
故选:C.
1 |
x |
7 |
∴(x+
1 |
x |
∴x2+
1 |
x2 |
(x-
1 |
x |
1 |
x2 |
x-
1 |
x |
3 |
故选:C.
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