1-cosx=sin x/2 cosx=cos^2x/2-sin^2 x/2 =2cos^2x/2 -1=1-2sin^2 x/2, далее 1-(1-2sin^2 x/2)=sin x/2 1-1+2sin^2 x/2=sin x/22sin^2 x/2=sin x/22sin x/2=1 Ответ:2sin x/2=1 ===> sin x/2=1/2