在三角形ABC中,若cos2A+cos2B+cos2C=-1,试判断三角形ABC的形状?
在三角形ABC中,若cos2A+cos2B+cos2C=-1,试判断三角形ABC的形状?
数学人气：336 ℃时间：2019-10-19 21:35:02
优质解答
由正弦定理得a/sinA=b/sinB,因为acosA=bcosB,所以sinAcosB-cosAsinB=sin（A-B）=0,所以∠A=∠B.cos2A+cos2B-cos2C=2cos2A-cos2C=2cos2A-cos2（180-A-B）=2cos2A-cos2（180-2A）=2cos2A-cos（360-4A）=2cos2A-cos4A=2...不活，题目是 在三角形ABC中，若cos2A+cos2B+cos2C=-1,试判断三角形ABC的形状？看清给可以，老大，但也给我了提示，我做出来了！哦
我来回答
类似推荐
猜你喜欢
- 15.6×12.5和0.58×9＋0.58这两题怎么简便计算啊!
- 2高明的大自然
- 3what kind of hell edu is this?I'm gonna hate it!
- 4他不能唱歌和跳舞英语怎么说
- 5-why didn't you try to get on the bus?_I tried to.but __I could ,it started to move.
- 6What day was it yesterday?What was the weather like yesterday?How are you today?H
- 7冬季取暖,若不采取任何其他措施,室内温度 ------- ,室内相对湿度 ------- .（填增大,减少或不变）.
- 827.it is believed that if a film is _____,it will ___ the audience.
- 9people can stay at home shopping whatever they want online he和
- 10()唉声叹气,()振作精神努力