Преобразуйте в произведение Cos2a+cos14a*cos6a+cos10a

Cos (2 * a) + cos (14 * a) + cos (6 * a) + cos (10 * a) = 2 * cos ((2 * a + 14 * a)/2) * cos ((2 * a - 14 * a)/2) + 2 * cos ((6 * a + 10 * a)/2) * cos ((6 * a - 10 * a)/2) = 2 * cos (16 * a/2) * cos (- 12 * a/2) + 2 * cos (16 * a/2) * cos (- 4 * a/2) = 2 * cos (8 * a) * cos (- 6 * a) + 2 * cos (8 * a) * cos (- 2 * a) = 2 * cos (8 * a) * cos (6 * a) + 2 * cos (8 * a) * cos (2 * a) = 2 * cos (8 * a) * (cos (6 * a) + cos (2 * a)) = 2 * cos (8 * a) * 2 * cos ((6 * a + 2 * a)/2) * cos ((6 * a - 2 * a)/2) = 4 * cos (8 * a) * cos (4 * a) * cos (2 * a).