AISHO
幼苗
共回答了17个问题采纳率:88.2% 举报
(1)
![](https://img.yulucn.com/upload/8/ce/8ceb278486371f9937b47b5c3a57ac85_thumb.jpg)
+
![](https://img.yulucn.com/upload/a/63/a63646804b7b82b47e486777dd0de25a_thumb.jpg)
=1
(2) -4< x
0 <
(3)当 x
0 =-
![](https://img.yulucn.com/upload/9/eb/9eb393a319f70cb25a44a6544a8a184c_thumb.jpg)
时, DE 的最大值为
本试题主要是考查了椭圆方程的求解以及结合圆的知识,求解圆与坐标轴的交点问题,以及直线与圆的位置关系的运用。
(1)∵椭圆
![](https://img.yulucn.com/upload/5/01/501a1cdf7a5d8ca127b68729a7db3a88_thumb.jpg)
+
![](https://img.yulucn.com/upload/a/1a/a1afa71e48bd2fda1019790395bc16d2_thumb.jpg)
=1( a > b >0)的离心率为
![](https://img.yulucn.com/upload/6/76/6768b8df1cf70be87e31dadf9010a771_thumb.jpg)
,且经过点 P (1,
![](https://img.yulucn.com/upload/0/74/07420aa88cd02c90cb65ff5f847a4422_thumb.jpg)
),
∴椭圆 C 的方程为
![](https://img.yulucn.com/upload/8/ce/8ceb278486371f9937b47b5c3a57ac85_thumb.jpg)
+
![](https://img.yulucn.com/upload/a/63/a63646804b7b82b47e486777dd0de25a_thumb.jpg)
=1。……… 5分
(2)易求得 F (1,0)。设 M ( x
0 , y
0 ),则
![](https://img.yulucn.com/upload/e/ff/eff7e240b49409fedcc42e2c5d369191_thumb.jpg)
+
![](https://img.yulucn.com/upload/b/ea/bea4d16e1294212dddaa7f29622e4a7f_thumb.jpg)
=1,
圆 M 的方程为( x - x
0 )
2 +( y - y
0 )
2 =(1- x
0 )
2 + y
0 2 ,
令 x =0,化简得 y
2 -2 y
0 y +2 x
0 -1=0,⊿=4 y
0 2 -4(2 x
0 -1)
2 >0……①。
将 y
0 2 =3(1-
![](https://img.yulucn.com/upload/e/ff/eff7e240b49409fedcc42e2c5d369191_thumb.jpg)
)代入①,得3 x
0 2 +8 x
0 -16<0,解出 -4< x
0 <
![](https://img.yulucn.com/upload/9/eb/9eb393a319f70cb25a44a6544a8a184c_thumb.jpg)
..........10分
(3)设 D (0, y
1 ), E (0, y
2 ),其中 y
1 < y
2 。由(2),得
DE = y
2 - y
1 =
![](https://img.yulucn.com/upload/4/ef/4ef9163518ddc48b9033b08d506a311a_thumb.jpg)
=
![](https://img.yulucn.com/upload/6/4a/64a76e1233dd5fda22edafbe3b754ade_thumb.jpg)
=
![](https://img.yulucn.com/upload/1/f5/1f59e626220f61adc73cbad9cbff3c04_thumb.jpg)
,
当 x
0 =-
![](https://img.yulucn.com/upload/9/eb/9eb393a319f70cb25a44a6544a8a184c_thumb.jpg)
时, DE 的最大值为
1年前
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