已知cos(a-π/3)=12/13,a属于(π/3,π/2),求cosa的值
问题描述:
已知cos(a-π/3)=12/13,a属于(π/3,π/2),求cosa的值
答
(12-5√3)/26
cos(a-π/3)=12/13
sin(a-π/3)=5/13
cosa=cos(a-π/3)cos(π/3)-sin(a-π/3)sin(π/3)
=12/13*1/2-5/13*√3/2
=(12-5√3)/26