альфа = х sinx \ cosx = корень из 5 sin^2 x \ cos^2 x = 5 sin^2 x\ 1-sin^2 x = 5 sin^2 х = 5 - 5sin^2 x 6sin^2 x = 5 sin^2 x = 5\6 12 * 5\ 6 = 10
5sin(11*П/12)=5sin(165)=5sin(180-15)=5sin(15)=1,2941
