题目内容
先化简,再求值:(
-
)÷
,其中x=2.
x+3 |
x2-3x |
x-1 |
x2-6x+9 |
9-x |
x2-3x |
解法一:原式=[
-
]÷
,(1分)
=[
-
]÷
,(2分)
=
÷
,
=
•
,(3分)
=-
.(4分)
∴当x=2时,原式=-
=1.(5分)
解法二:(
-
)÷
,
=[
-
]•
,(1分)
=
•
-
•
,(2分)
=
-
,(3分)
=-
.(4分)
∴当x=2时,原式=-
=1.(5分)
x+3 |
x(x-3) |
x-1 |
(x-3)2 |
9-x |
x(x-3) |
=[
(x+3)(x-3) |
x(x-3)2 |
x(x-1) |
x(x-3)2 |
9-x |
x(x-3) |
=
x2-9-x2+x |
x(x-3)2 |
9-x |
x(x-3) |
=
x-9 |
x(x-3)2 |
x(x-3) |
9-x |
=-
1 |
x-3 |
∴当x=2时,原式=-
1 |
2-3 |
解法二:(
x+3 |
x2-3x |
x-1 |
x2-6x+9 |
9-x |
x2-3x |
=[
x+3 |
x(x-3) |
x-1 |
(x-3)2 |
x(x-3) |
9-x |
=
x+3 |
x(x-3) |
x(x-3) |
9-x |
x-1 |
(x-3)2 |
x(x-3) |
9-x |
=
x+3 |
9-x |
x(x-1) |
(x-3)(9-x) |
=-
1 |
x-3 |
∴当x=2时,原式=-
1 |
2-3 |
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