cos²73°+cos²47°+cos73°cos47°的值是多少
来源:学生作业帮助网 编辑:作业帮 时间:2024/06/27 18:30:48
![cos²73°+cos²47°+cos73°cos47°的值是多少](/uploads/image/z/13301150-14-0.jpg?t=cos%26%23178%3B73%C2%B0%2Bcos%26%23178%3B47%C2%B0%2Bcos73%C2%B0cos47%C2%B0%E7%9A%84%E5%80%BC%E6%98%AF%E5%A4%9A%E5%B0%91)
cos²73°+cos²47°+cos73°cos47°的值是多少
cos²73°+cos²47°+cos73°cos47°的值是多少
cos²73°+cos²47°+cos73°cos47°的值是多少
cos²73°+cos²47°+cos73°cos47°
=1/2(cos146-1)+1/2(cos94-1)+cos73°cos47°
=1/2(cos146+cos94)+cos73°cos47°-1
=cos120*cos26+1/2(cos120+cos26)-1(和差化积,积化和差)
=-1/2*cos26-1/4+1/2*cos26-1
=-5/4