大兵_张
花朵
共回答了14个问题采纳率:85.7% 举报
(1)椭圆C的标准方程为
![](https://img.yulucn.com/upload/c/b4/cb42709d660f44325d89e11eef29f038_thumb.jpg)
,抛物线E的标准方程为
![](https://img.yulucn.com/upload/2/4e/24e2d425169ceb4475930741775388d1_thumb.jpg)
.(2)
![](https://img.yulucn.com/upload/a/f1/af19be4581d81d21250fad23193d3e43_thumb.jpg)
有最小值为16.
试题分析:(1)由于椭圆上任意一点到焦点的距离都等于
![](https://img.yulucn.com/upload/9/cc/9cc2c2e17f0d589307ec2a72ea337f51_thumb.jpg)
,所以
![](https://img.yulucn.com/upload/3/29/3295ed548d3084cdc5b6ea47cbd5d4c0_thumb.jpg)
,
![](https://img.yulucn.com/upload/e/df/edf9d87dbbcd15adb862af520837af67_thumb.jpg)
,由此即得椭圆的标准方程
![](https://img.yulucn.com/upload/c/b4/cb42709d660f44325d89e11eef29f038_thumb.jpg)
.椭圆右顶点 F 的坐标为(1,0),所以抛物线 E 的标准方程为
![](https://img.yulucn.com/upload/2/4e/24e2d425169ceb4475930741775388d1_thumb.jpg)
.(2)设
![](https://img.yulucn.com/upload/5/50/55057fc3d89b1f940a2da85ec0d13380_thumb.jpg)
,
![](https://img.yulucn.com/upload/c/93/c93245c7f1f9009741ddd7b4c9a0276b_thumb.jpg)
,
![](https://img.yulucn.com/upload/0/a8/0a89c661bd52f3d7d543c947bd84f66b_thumb.jpg)
,
![](https://img.yulucn.com/upload/3/10/310f25d04ecab3f05f8a17661d2dcd2e_thumb.jpg)
,则
![](https://img.yulucn.com/upload/3/96/396046ae6aaaea015aa774ec4e765abc_thumb.jpg)
.再设 l
1 的方程:
![](https://img.yulucn.com/upload/3/b0/3b00e80f120d66ad4bf21990bef9ae8b_thumb.jpg)
, l
2 的方程
![](https://img.yulucn.com/upload/b/c3/bc3dc06c05aef259295f5fc5909ed3f3_thumb.jpg)
,用韦达定理将上式表示为
![](https://img.yulucn.com/upload/6/c8/6c8c32b25fce158c5abbffec03f12a49_thumb.jpg)
即可求得其最小值.
试题解析:(1)设椭圆的标准方程为
![](https://img.yulucn.com/upload/2/8c/28c29ed2f786cdda1eaf4b29b29d7801_thumb.jpg)
( a > b >0),焦距为2 c ,
则由题意得 c =
![](https://img.yulucn.com/upload/a/3b/a3b328655b434a0a5725bde7d9260ef3_thumb.jpg)
,
![](https://img.yulucn.com/upload/3/29/3295ed548d3084cdc5b6ea47cbd5d4c0_thumb.jpg)
,
∴
![](https://img.yulucn.com/upload/e/df/edf9d87dbbcd15adb862af520837af67_thumb.jpg)
,
∴椭圆 C 的标准方程为
![](https://img.yulucn.com/upload/c/b4/cb42709d660f44325d89e11eef29f038_thumb.jpg)
.4分
∴右顶点 F 的坐标为(1,0).
设抛物线 E 的标准方程为
![](https://img.yulucn.com/upload/3/b1/3b11000d68e131c9758bb785bc90da72_thumb.jpg)
,∴
![](https://img.yulucn.com/upload/e/9f/e9f57a82826b54f55eed4bfa0f58cf86_thumb.jpg)
,
∴抛物线 E 的标准方程为
![](https://img.yulucn.com/upload/2/4e/24e2d425169ceb4475930741775388d1_thumb.jpg)
. 6分
(2)设 l
1 的方程:
![](https://img.yulucn.com/upload/3/b0/3b00e80f120d66ad4bf21990bef9ae8b_thumb.jpg)
, l
2 的方程
![](https://img.yulucn.com/upload/b/c3/bc3dc06c05aef259295f5fc5909ed3f3_thumb.jpg)
,
![](https://img.yulucn.com/upload/5/50/55057fc3d89b1f940a2da85ec0d13380_thumb.jpg)
,
![](https://img.yulucn.com/upload/c/93/c93245c7f1f9009741ddd7b4c9a0276b_thumb.jpg)
,
![](https://img.yulucn.com/upload/0/a8/0a89c661bd52f3d7d543c947bd84f66b_thumb.jpg)
,
![](https://img.yulucn.com/upload/3/10/310f25d04ecab3f05f8a17661d2dcd2e_thumb.jpg)
,
由
![](https://img.yulucn.com/upload/a/02/a0213dec681de19c5b0c523b41a343da_thumb.jpg)
消去 y 得:
![](https://img.yulucn.com/upload/1/e2/1e28aaaac58bf18af3da985801f177d3_thumb.jpg)
,
∴
![](https://img.yulucn.com/upload/e/6b/e6bb2e24e60382bbc941d60ea9bbbeda_thumb.jpg)
.
由
![](https://img.yulucn.com/upload/e/ec/eec0ff1819553a4d7cdfaea0631903eb_thumb.jpg)
消去 y 得:
![](https://img.yulucn.com/upload/a/ad/aadc218f90bf3d577406c0a86700b5fc_thumb.jpg)
,
∴
![](https://img.yulucn.com/upload/1/05/1053e9bf95a2e851a1dfe159e2b597d9_thumb.jpg)
9分
∴
1年前
4