题目
题型:不详难度:来源:
![](http://img.shitiku.com.cn/uploads/allimg/20191023/20191023142000-53567.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191023/20191023142000-41478.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191023/20191023142000-64141.jpg)
A.±![]() | B.±![]() |
C.±![]() | D.±![]() |
答案
解析
![](http://img.shitiku.com.cn/uploads/allimg/20191023/20191023142000-53567.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191023/20191023142000-41478.png)
∴kAB=
![](http://img.shitiku.com.cn/uploads/allimg/20191023/20191023142001-40326.png)
设l方程为y=-
![](http://img.shitiku.com.cn/uploads/allimg/20191023/20191023142001-70550.png)
则C
![](http://img.shitiku.com.cn/uploads/allimg/20191023/20191023142001-23923.png)
DF方程为y=kDFx+m,
由
![](http://img.shitiku.com.cn/uploads/allimg/20191023/20191023142001-32070.png)
得(b2+a2
![](http://img.shitiku.com.cn/uploads/allimg/20191023/20191023142001-55380.png)
∵DF与椭圆相切,
∴Δ=(2a2mkDF)2-4(b2+a2
![](http://img.shitiku.com.cn/uploads/allimg/20191023/20191023142001-55380.png)
得
![](http://img.shitiku.com.cn/uploads/allimg/20191023/20191023142001-55380.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191023/20191023142002-87693.png)
直线CE的方程为y=kCE(x-
![](http://img.shitiku.com.cn/uploads/allimg/20191023/20191023142002-90875.png)
由
![](http://img.shitiku.com.cn/uploads/allimg/20191023/20191023142002-38053.png)
得(b2+a2
![](http://img.shitiku.com.cn/uploads/allimg/20191023/20191023142002-42490.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191023/20191023142002-90437.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191023/20191023142003-53899.png)
∵CE与椭圆相切,
∴Δ=(-
![](http://img.shitiku.com.cn/uploads/allimg/20191023/20191023142002-90437.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191023/20191023142002-42490.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191023/20191023142003-53899.png)
化简得
![](http://img.shitiku.com.cn/uploads/allimg/20191023/20191023142002-42490.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191023/20191023142003-79770.png)
∴
![](http://img.shitiku.com.cn/uploads/allimg/20191023/20191023142001-55380.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191023/20191023142002-42490.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191023/20191023142002-87693.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191023/20191023142003-28776.png)
=
![](http://img.shitiku.com.cn/uploads/allimg/20191023/20191023142003-57252.png)
∴kDF·kCE=±
![](http://img.shitiku.com.cn/uploads/allimg/20191023/20191023142001-66492.png)
核心考点
试题【如图所示,已知A,B分别为椭圆+=1(a>b>0)的右顶点和上顶点,直线l∥AB,l与x轴、y轴分别交于C,D两点,直线CE,DF为椭圆的切线,则C】;主要考察你对椭圆的定义与方程等知识点的理解。[详细]
举一反三
![](http://img.shitiku.com.cn/uploads/allimg/20191023/20191023141950-91462.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191023/20191023141950-15281.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191023/20191023141950-15291.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191023/20191023141944-60978.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191023/20191023141945-21366.jpg)
A.![]() | B.![]() | C.![]() | D.![]() |
![](http://img.shitiku.com.cn/uploads/allimg/20191023/20191023141934-16105.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191023/20191023141934-79453.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191023/20191023141934-63650.png)
A.![]() ![]() | B.![]() ![]() |
C.![]() ![]() | D.![]() ![]() |
![](http://img.shitiku.com.cn/uploads/allimg/20191023/20191023141927-70756.jpg)
A.3 | B.2 | C.![]() | D.![]() |
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