设α为锐角,若cos(α+π/6)=4/5,则sin(2α+π/6)=
人气:384 ℃ 时间:2019-12-08 19:50:16
解答
由cos(α+π/6)=4/5 推导出→sin(α+π/6)=3/5
引入一个sin(2α+π/3)
=sin2(α+π/6)
=2sin(α+π/6)cos(α+π/6)
=2×3/5×4/5
=24/25 推导出→cos (2α+π/3)=7/25
sin(2α+π/6)=sin[(2α+π/3)-π/6]
=sin (2α+π/3)cos π/6-cos (2α+π/3)sinπ/6
=24/25×(根号3分之2)- 7/25×2分之一
=(24根号3-7)/50
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