Найдите cos (a+b), cos2a, sin 2b, если sina = 8/17, cos b=3/5

Cos (a+b) = cosa. cosb-sina. sinb,

cos2a = cos kv a - sin kv a

sin2b = 2. sinb. cosb.

Nado znat sinb a cos a.

sin kv b = 1 - cos kv b = 1-9/25=16/25, sinb = 4/5

cos kv a = 1-sin kv a = 1-64/289 = 225/289, cos a = 15/17

cos (a+b) = 15/17.3/5 - 8/17.4/5 =

cos 2a = 225/289 - 64/289 = 161/289

sin2b = 2. 4/5.3/5 = 24/25