题目内容
先化简，再求值：
÷
•
，其中x=tan60°-4cos60°．
| 9-x2 |
| x2+4x+4 |
| x-3 |
| 2x+4 |
| x-1 |
| x+3 |
| 9-x2 |
| x2+4x+4 |
| x-3 |
| 2x+4 |
| x-1 |
| x+3 |
=
| (3+x)(3-x) |
| (x+2)2 |
| 2(x+2) |
| x-3 |
| x-1 |
| x+3 |
=-
| 2(x-1) |
| x+2 |
∵x=tan60°-4cos60°=
| 3 |
| 1 |
| 2 |
| 3 |
∴原式=-
2(
| ||
|
=-（2-2
| 3 |
=2
| 3 |
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