sina=4/5,cosa=-3/5
sin(2α+2π/3)
=sin2acos2π/3+cos2asin2π/3
=-1/2sin2a+√3/2cos2a
=-sinacosa+√3/2(cos^2a-sin^2a)
=12/25-√3/2*7/25
=(24-7√3)/50
sina=4/5,cosa=-3/5
sin(2α+2π/3)
=sin2acos2π/3+cos2asin2π/3
=-1/2sin2a+√3/2cos2a
=-sinacosa+√3/2(cos^2a-sin^2a)
=12/25-√3/2*7/25
=(24-7√3)/50