题目内容
先化简,再求值:
(1)(
-
)÷
,其中x=
+1
(2)(1+
)÷
,其中x=
+3
(3)
÷(x+2-
),其中x=
-4
(4)
÷(
-x-2),其中x=
-2.
(1)(
x+1 |
x2-x |
x |
x2-2x+1 |
1 |
x |
2 |
(2)(1+
x-3 |
x+3 |
2x |
x2-9 |
3 |
(3)
4-x |
x-2 |
12 |
x-2 |
3 |
(4)
x-3 |
2x-4 |
5 |
x-2 |
3 |
(1)(
-
)÷
,
=
•x-
•x,
=
-
,
=
,
=-
,
把x=
+1代入原式=-
=9
;
(2)(1+
)÷
,
=
×
=x-3;
把x=
+3代入原式=
+3-3=
;
(3)
÷(x+2-
),
=
÷
=
×
=-
,
把x=
-4代入原式=-
=-
;
(4)
÷(
-x-2),
=
÷
=
×
=-
把x=
-2代入上式得:
原式=-
=
.
x+1 |
x2-x |
x |
x2-2x+1 |
1 |
x |
=
x+1 |
x(x-1) |
x |
(x-1)2 |
=
x+1 |
x-1 |
x2 |
(x-1)2 |
=
x2-1-x2 |
(x-1)2 |
=-
1 |
(x-1)2 |
把x=
2 |
1 | ||
(
|
1 |
2 |
(2)(1+
x-3 |
x+3 |
2x |
x2-9 |
=
2x |
x+3 |
(x+3)(x-3) |
2x |
=x-3;
把x=
3 |
3 |
3 |
(3)
4-x |
x-2 |
12 |
x-2 |
=
4-x |
x-2 |
(x+4)(x-4) |
x-2 |
=
4-x |
x-2 |
x-2 |
(x+4)(x-4) |
=-
1 |
x+4 |
把x=
3 |
1 | ||
|
| ||
3 |
(4)
x-3 |
2x-4 |
5 |
x-2 |
=
x-3 |
2(x-2) |
9-x2 |
x-2 |
=
x-3 |
2(x-2) |
x-2 |
(3+x)(3-x) |
=-
1 |
2((3+x) |
把x=
3 |
原式=-
1 | ||
2(3+
|
1-
| ||
4 |
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