已知cos(a-π/3)=12/13,a属于(π/3,π/2),求cosa的值
人气：456 ℃ 时间：2020-04-10 07:56:42
解答
(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
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