题目
题型:不详难度:来源:
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061051-66056.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061051-27841.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061052-64532.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061052-73565.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061052-25048.gif)
(1)求
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061052-70096.gif)
(2)在
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061052-31029.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061053-41479.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061053-57401.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061053-83904.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061052-70096.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061052-31029.gif)
答案
(1)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061053-45996.gif)
(2)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061054-65674.gif)
解析
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061054-69636.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061054-10264.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061054-60602.gif)
由题意知
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061055-56928.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061055-53308.gif)
(2)由于
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061055-48564.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061052-70096.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061055-77609.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061055-97580.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061056-88414.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061056-42905.gif)
由余弦定理得
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061056-51202.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061056-59691.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061057-87134.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061057-21229.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061057-29222.gif)
核心考点
举一反三
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061047-11998.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061047-81950.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061047-30591.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061047-26553.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061047-73066.gif)
的中点,且
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061048-54468.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061048-12938.gif)
已知△ABC顶点的直角坐标分别为A(3,4),B(0,0),C(c,0)
(1)若c=5,求sin∠A的值;
(2)若∠A是钝角,求c的取值范围。
在长方形ABEF中,D,C分别是AF和BE的中点,M和N分别是AB和AC的中点,AF=2AB=2a,将平面DCEF沿着DC折起,使角
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061035-57986.gif)
求证:
(1)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061035-32190.gif)
(2)当FG=GD时,求证:GA
题型:平面FMC。
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061035-71899.jpg)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061036-71688.jpg)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061035-71899.jpg)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061036-71688.jpg)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061029-64745.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061029-17403.gif)
(1)求
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061030-92885.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061030-12849.gif)
(2)若
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061030-23157.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061030-29653.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061027-97181.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020061027-97181.gif)