Сделайте, . 35 поинтов​

2

cos(3a/2)*cos(a/2)=1/2

cos(3a/2)*cos(a/2) =

= (1/2) * ( cos(3a/2 + a/2) + cos (3a/2 - a/2) ) =

= (1/2) * (cos (4a/2) + cos (2a/2) ) =

= (1/2) * (cos (2a) + cos(a)) =

= (1/2) * (2 cos² a - 1 + cos a) = 1/2

(2 cos² a - 1 + cos a) = (1/2) : (1/2)

(2 cos² a - 1 + cos a) = 1 →

→ 2 * (2 cos² a + cos a - 1) = 2*1 = 2