sin 15° = sin 1/2(30°) =

sin 1/2a = √{(1 - cos a)/2}maka,
sin 1/2(30) = √{(1 - cos 30)/2}
sin 15 = √{(1 - 1/2 √3)/2}
= √{(2 - √3)/2 x 1/2}
= √{(2-√3)/4}
= 1/2 x √(2-√3)