题目内容
化简求值(1)已知x=
1 | ||
2+
|
x | ||
2+
|
| ||
x2-x |
(2)(2
|
|
|
xy |
分析:(1)首先将x分母有理化,再化简代数式,代入求值即可,注意
=|a|;
(2)首先化简代数式,再化简即可求得结果.
a2 |
(2)首先化简代数式,再化简即可求得结果.
解答:解:(1)∵x=
=2-
,
∴x-1=1-
<0,
∴
-
,
=
-
,
=(2-
)2-
,
=7-4
+
,
=7-4
+2+
,
=9-3
;
(2)∵x=1,y=2,
∴(2
-
+
)
,
=2y-x+1,
=2×2-1+1,
=4.
1 | ||
2+
|
3 |
∴x-1=1-
3 |
∴
x | ||
2+
|
| ||
x2-x |
=
2-
| ||
2+
|
| ||
x(x-1) |
=(2-
3 |
1-x |
x(x-1) |
=7-4
3 |
1 |
x |
=7-4
3 |
3 |
=9-3
3 |
(2)∵x=1,y=2,
∴(2
|
|
|
xy |
=2y-x+1,
=2×2-1+1,
=4.
点评:此题考查二次根式的运算.注意化简求值的问题,需要先化简代数式,再代入求值.

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