题目内容
先化简,再求值:
(1)(
-
)÷
,其中x=1+
,y=1-
.
(2)
+6
-2x
,代入一个合适的x的值求值.
(1)(
1 |
x-y |
1 |
x+y |
2y |
x2-2xy+y2 |
2 |
2 |
(2)
2 |
3 |
9x |
|
|
(1)原式=
•
=
,
当x=1+
,y=1-
时,原式=
=
;
(2)原式=2
+3
-2
=3
,
当x=9时,原式=9.
x+y-x+y |
(x+y)(x-y) |
(x-y)2 |
2y |
x-y |
x+y |
当x=1+
2 |
2 |
2
| ||
2 |
2 |
(2)原式=2
x |
x |
x |
x |
当x=9时,原式=9.
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