题目
题型:不详难度:来源:
答案
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105004402-23931.png)
解析
试题分析:如图所示,△ABC是等边三角形,OB=2,过点O作OD⊥BC于点D,则BD=
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105004402-85647.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105004402-37305.png)
∵△ABC是等边三角形,
∴∠OBD=30°,
在Rt△OBD中,
∵cos∠OBD=
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105004402-81531.png)
∴BD=OB•cos30°=2×
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105004403-12244.png)
∴BC=2BD
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105004403-93007.png)
核心考点
举一反三
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105004353-87438.png)
(1)画出△A1OB1;
(2)点A1的坐标为 ;
(3)点A旋转到点A1所经过的路线长为_____________.(结果保留π)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105004347-91100.jpg)
(1)请你按下面步骤画图(画图或作辅助线时先使用铅笔画出,确定后必须使用黑色字迹的签字笔描黑);
第一步,过点A作∠BAC的角平分线,交⊙O于点D;
第二步,过点D作AC的垂线,交AC的延长线于点E.
第三步,连接BD.
(2)求证:DE是⊙O的切线;
(3)如图AD=5,AE=4,求⊙O的直径.
A.12π | B.15π | C.24π | D.30π |
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105004339-46370.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105004339-76330.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105004339-46370.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105004339-90317.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191105/20191105004340-45214.jpg)