Допоможіть обчислити Cos ( 11пі/12)- СOS (5пі/12)

Спасибо)))

cos(11π/12)-cos(5π/12)=-2sin((11π/12+5π/12)/2)*sin((11π/12-5π/12)/2)==-2sin(16π/24)*sin(6π/24)=-2sin(2π/3)*sin(π/4)=-2*√3/2*√2/2=-√6/2.