在△ABC中,角A,B,C的对边分别为a,b,c.
(1)若a=3c,b=
,cosB=
,求c的值;
(2)若
,求cosB的值.
(1)若a=3c,b=
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/cf298f00799cbf34b4db26f5f63af92f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/bf31876698721a199c7c53c6b320aa86.png)
(2)若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a8a221e6868c8b15c1d0df8984626432.png)
2020高三·全国·专题练习 查看更多[1]
(已下线)专题4.6 正弦定理和余弦定理(精讲)-2021年高考数学(文)一轮复习学与练
更新时间:2020-10-19 08:55:48
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解题方法
【推荐1】在
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![](https://staticzujuan.xkw.com/quesimg/Upload/formula/cf298f00799cbf34b4db26f5f63af92f.png)
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