Cos (pi/3 - a), если cos a = 3/4, ae (0; pi/2)

Question

Cos (pi/3 - a), если cos a = 3/4, ae (0; pi/2)

Answer 1

( Sin²α = 1 - Cos²α= 1 - 9/16 = 7/16, ⇒Sinα =√7/4)
Cos(π/3 -α) = Сosπ/3Cosα + Sin π/3 Sinα = 
=1/2·Cosα + √3/2·Sinα=1/2·3/4 + √3/2·√7/4 = 3/8 + √21/8