sina=-sqrt(1-cos^2 a)=-sqrt(1-64/289)=-sqrt(225/289)=-15/17
sin2a=2sinacosa=2*(-15/17)*8/17=-2*(120/289)=-240/289
sina=-sqrt(1-cos^2 a)=-sqrt(1-64/289)=-sqrt(225/289)=-15/17
sin2a=2sinacosa=2*(-15/17)*8/17=-2*(120/289)=-240/289