设a为第二象限角,且sina=3\5,求sin(37π\6-2a)
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![设a为第二象限角,且sina=3\5,求sin(37π\6-2a)](/uploads/image/z/8561674-10-4.jpg?t=%E8%AE%BEa%E4%B8%BA%E7%AC%AC%E4%BA%8C%E8%B1%A1%E9%99%90%E8%A7%92%2C%E4%B8%94sina%3D3%5C5%2C%E6%B1%82sin%2837%CF%80%5C6-2a%29)
设a为第二象限角,且sina=3\5,求sin(37π\6-2a)
设a为第二象限角,且sina=3\5,求sin(37π\6-2a)
设a为第二象限角,且sina=3\5,求sin(37π\6-2a)
sin(37π/6-2a)
=sin(π/6-2a)
=cos2a/2-根3sin2a/2
a为第二象限角,且sina=3/5,cosa = -4/5
cos2a=1-2sinasina=7/25 sin2a=2sinacosa=-24/25