题目
题型:不详难度:来源:
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002547-60105.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002547-73709.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002548-39995.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002548-46467.png)
(1)当
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002547-60105.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002547-73709.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002548-39995.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002548-12337.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002547-60105.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002547-73709.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002548-39995.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002548-67727.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002549-76307.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002549-66648.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002549-54990.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002549-34851.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002547-73709.png)
(2)若
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002550-11265.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002547-60105.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002547-73709.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002548-39995.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002547-60105.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002550-17194.png)
答案
解析
试题分析:(1)本题属于解三角形问题,它是“已知两边及一边所对的角,求第三边”的问题,解决这个问题可以有两种方法,一种是先用正弦定理求出已知两边所对的角中未知的一角,从而可求得第三角,然后用余弦定理求出第三边,也可以直接用余弦定理列出待求边的方程,通过解方程求出第三边;(2)首先要证明长为
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002547-60105.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002547-73709.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002548-39995.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002550-86909.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002550-67598.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002550-65187.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002551-52196.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002551-85391.png)
试题解析:(1)解:由
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002551-72149.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002552-49740.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002552-99677.png)
(2)证:由
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002552-36121.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002552-80748.png)
所以
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002552-27835.png)
也就是
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002553-47922.png)
因此长为
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002553-47909.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002548-12337.png)
在
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002548-12337.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002553-80627.png)
即
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002553-83728.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002554-36142.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002554-58223.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002554-46351.png)
所以边
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002547-60105.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002550-17194.png)
核心考点
试题【已知、、为正实数,.(1)当、、为的三边长,且、、所对的角分别为、、.若,且.求的长;(2)若.试证明长为、、的线段能构成三角形,而且边的对角为.】;主要考察你对余弦定理等知识点的理解。[详细]
举一反三
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002536-20069.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002537-37669.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002537-76768.png)
A.![]() | B.![]() | C.![]() | D.![]() |
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002530-22085.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002530-70987.png)
A.1:1 | B.1:2 | C.1:4 | D.4:3 |
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002522-26418.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002522-26418.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002515-21468.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002515-37946.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002516-10032.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002516-53520.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002516-15253.png)
A.![]() | B.![]() | C.![]() | D.![]() |
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002510-61329.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002510-44260.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191020/20191020002510-76858.png)
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