cos(-165)解答过程怎样,急需
来源:学生作业帮 编辑:搜搜做题作业网作业帮 分类:数学作业 时间:2024/06/14 15:38:59
cos(-165)解答过程怎样,急需
诱导公式
cos(-x)=cosx
cos(a+b)=cosacosb-sinasinb
所以cos(-165)
=cos165
=cos(135+30)
=cos135cos30-sin135sin30
=(-√2/2)(√3/2)-(√2/2)(1/2)
=-(√6+√2)/4
cos(-x)=cosx
cos(a+b)=cosacosb-sinasinb
所以cos(-165)
=cos165
=cos(135+30)
=cos135cos30-sin135sin30
=(-√2/2)(√3/2)-(√2/2)(1/2)
=-(√6+√2)/4