牛一白也
春芽
共回答了14个问题采纳率:85.7% 举报
(1)∵O(0,0),A(6,2
![](https://img.yulucn.com/upload/f/8b/f8b80a7d597e71098b5377d74daa6d2d_thumb.jpg)
),
∴直线OA的方程斜率为
![](https://img.yulucn.com/upload/3/b9/3b9e984eacd5e5e8271d20c49c2afb40_thumb.jpg)
=
![](https://img.yulucn.com/upload/1/ee/1ee323d89b9c2ffa4fb03d64112feaba_thumb.jpg)
,
∴线段OA垂直平分线的斜率为﹣
![](https://img.yulucn.com/upload/6/0c/60c763316416e27db37597c60d12d5ab_thumb.jpg)
,
又线段AO的中点坐标为(3,
![](https://img.yulucn.com/upload/8/4b/84b0bb511f2cebe608daeeceee272e9d_thumb.jpg)
),
∴线段OA垂直平分线的方程为y﹣
![](https://img.yulucn.com/upload/9/38/938b00d3894d6b5b9aeee0ce84b0b2eb_thumb.jpg)
=﹣
![](https://img.yulucn.com/upload/0/0f/00f384d5c33c3ea477c1315f2004c676_thumb.jpg)
(x﹣3),即
![](https://img.yulucn.com/upload/2/80/28015ad65eb84530449d01e9322322ec_thumb.jpg)
x+y﹣4
![](https://img.yulucn.com/upload/0/83/08383a006b4e2e2f1e0234a49a08e692_thumb.jpg)
=0①,
又线段OB的垂直平分线为x=4②,
∴将②代入①解得:y=0,
∴圆心C的坐标为(4,0),
又|OC|=4,即圆C的半径为4,
则圆C的方程为:(x﹣4)
2 +y
2 =16;
(2)显然切线方程的斜率存在,设切线l的斜率为k,又切线过(2,6),
∴切线l的方程为y﹣6=k(x﹣2),即kx﹣y+6﹣2k=0,
∴圆心到切线的距离d=r,即
![](https://img.yulucn.com/upload/6/7b/67b74461d1994d0f20c5de7bdcc1af10_thumb.jpg)
=4,
解得:k=
![](https://img.yulucn.com/upload/6/09/609f6edda76b128b8c6c2e4f8e1b3ce6_thumb.jpg)
,
则切线l的方程为:y﹣6=
![](https://img.yulucn.com/upload/a/26/a26d2d0f307f3df9af71f4a372caf114_thumb.jpg)
(x﹣2);
(3)当直线l的斜率不存在时,显然直线x=2满足题意;
当直线l的斜率存在时,设斜率为k,又直线l过(2,6),
∴切线l的方程为y﹣6=k(x﹣2),
即kx﹣y+6﹣2k=0,
又弦长为4
![](https://img.yulucn.com/upload/7/82/7820569775f0eb85fb672c37f2378070_thumb.jpg)
,半径r=4,
∴圆心到切线的距离d=
![](https://img.yulucn.com/upload/c/84/c84251b5b38d0e21f845a29319b42a69_thumb.jpg)
=2,即
![](https://img.yulucn.com/upload/1/a7/1a74e430f61cb7797d65edbcf5ca9f1e_thumb.jpg)
=2,
解得:k=﹣
![](https://img.yulucn.com/upload/1/94/1948f6466b661abe90d6f674b4da83ff_thumb.jpg)
,
∴直线l的方程为y﹣6=﹣
![](https://img.yulucn.com/upload/a/74/a7400f5ec10fd50bc29eb31ee5c5f7bb_thumb.jpg)
(x﹣2),
即4x+3y﹣26=0,
综上,直线l的方程为x=2或4x+3y﹣26=0.
1年前
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