xiaohuya
幼苗
共回答了18个问题采纳率:94.4% 举报
(Ⅰ)设P(x,y),A(x
1 ,y
1 ),B(x
2 ,y
2 ),
∵P是线段AB的中点,
∴
![](https://img.yulucn.com/upload/2/6f/26fafca798989bbf28d1a7e5ad153973_thumb.jpg)
,
∵A,B分别是直线y=
![](https://img.yulucn.com/upload/e/40/e40e1f76221df16cc145f35b684b2929_thumb.jpg)
x和y=-
![](https://img.yulucn.com/upload/e/40/e40e1f76221df16cc145f35b684b2929_thumb.jpg)
x上的点,
∴
![](https://img.yulucn.com/upload/9/85/98554848397d7802900ebc27003d8a6d_thumb.jpg)
和
![](https://img.yulucn.com/upload/6/6c/66c54fb80d4fed1b559882684a43e213_thumb.jpg)
,
∴
![](https://img.yulucn.com/upload/b/c6/bc6486fc569f87d72445dda7dc26162e_thumb.jpg)
,
又
![](https://img.yulucn.com/upload/3/88/388834eae04e4a2e3bbefb192ad85602_thumb.jpg)
,
∴
![](https://img.yulucn.com/upload/8/b0/8b0456568ed72506ed0254f7ab4763fc_thumb.jpg)
,
∴
![](https://img.yulucn.com/upload/6/90/690cde791536275a5ff7e97b9eca6775_thumb.jpg)
,
∴动点P的轨迹C的方程为
![](https://img.yulucn.com/upload/1/c1/1c1bb9a58388a019b993982bdfbc8d1b_thumb.jpg)
。
(Ⅱ)依题意,直线l的斜率存在,故可设直线l的方程为y=k(x-1),
设M(x
3 ,y
3 ),N(x
4 ,y
4 ),R(0,y
5 ),
则M,N两点坐标满足方程组
![](https://img.yulucn.com/upload/e/b7/eb75fe3e8f5ac669485e882ca2166cc0_thumb.jpg)
,
消去y并整理,得
![](https://img.yulucn.com/upload/2/65/265277ee7d5feb135c7410a92c1f309b_thumb.jpg)
,
∴
![](https://img.yulucn.com/upload/3/bd/3bdb6577a4fd4ce709bc3d6cb49005a2_thumb.jpg)
,①
![](https://img.yulucn.com/upload/7/de/7de8e30230c51de68a249bc80a619cc8_thumb.jpg)
,②,
∵
![](https://img.yulucn.com/upload/2/19/2195d5ded835caff854096b53256ca0d_thumb.jpg)
,
∴
![](https://img.yulucn.com/upload/2/f4/2f4dc5ffd79250bf3b33cd3ee04f0e63_thumb.jpg)
,
即
![](https://img.yulucn.com/upload/1/19/1195608d82d74139b70fcd440bc74c3f_thumb.jpg)
,
∴
![](https://img.yulucn.com/upload/d/30/d30ea0500d5aaac25b8c938e3e5e2cfa_thumb.jpg)
,
∵l不与x轴垂直,
∴
![](https://img.yulucn.com/upload/6/75/675f4e4d81ed7f31fe4863ce02b517df_thumb.jpg)
,∴
![](https://img.yulucn.com/upload/8/ca/8ca8ee74a6eebf790e5cca1c1c1cca17_thumb.jpg)
,同理
![](https://img.yulucn.com/upload/d/08/d086e8974090bd6523dc449070e549df_thumb.jpg)
,
∴
![](https://img.yulucn.com/upload/4/74/474a1aff133be0f0cd2b12efd5c488cc_thumb.jpg)
,
将①②代入上式,可得
![](https://img.yulucn.com/upload/2/07/20743fd7e19e4e60f585e6b65666203b_thumb.jpg)
。
1年前
8