sin(π/6＋a)=sin[π/2－(π/3－a)]=cos(π/3－a)
因sin(π/6＋a)=3/5,则：cos(π/3－a)=3/5
则cos（α－π／3）＝cos(π/3－a)=3/5
sin（π／6＋α）＝3／5,则cos（α－π／3）＝
sin（π／6＋α）＝3／5,则cos（α－π／3）＝
不理解 cos（α－π／3）＝cos(π/3－a)=3/5
不理解 cos（α－π／3）＝cos(π/3－a)=3/5
数学人气：950 ℃时间：2020-02-04 08:21:29
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