cos(a+π/6)=3/5,
a是锐角
∴sin(a+π/6)>0
∴sin(a+π/6)=4/5
sin(2a+π/3)
=sin[2(a+π/6)]
正弦2倍角公式得
=2sin(a+π/6)cos(a+π/6)
=2*4/5*3/5
=24/25
手机提问的朋友在客户端右上角评价点【满意】即可