Выражение cos (p/6-a) + sin (p/6 +a)

Cos (π/6-a) + Sin (π/6 +a) =Cos (π/6-a)  + Cos(π/2 - π/6 -a)=
=Cos (π/6-a)  + Cos(π/3 -α) = 2Сos(π/4-α) *Cosπ/12=
=2*√2/2(Cosα + Sinα)*Sinπ/12= √2(Cosα + Sinα)*Sinπ/12