sin x/2- cos x/2=1/3,
(sinx/2-cosx/2)^2=1/9
sin(x/2)^2+cos(x/2)^2-2sinx/2cosx/2=1/9
sin(x/2)^2+cos(x/2)^2=1
2sinx/2cosx/2=sinx
所以
1-sinx=1/9
sin=1-1/9
=8/9