题目
sin(75°+a)=1/3,则cos(15°-a)=
提问时间:2021-02-19
答案
sin(π/2-α)=cos α
sin(90°-α)=cos α
cos(15°-a)
=sin(90°-(15°-a))
=sin(90°-15°+a)
=sin(75°+a)
=1/3
sin(90°-α)=cos α
cos(15°-a)
=sin(90°-(15°-a))
=sin(90°-15°+a)
=sin(75°+a)
=1/3
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