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)

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