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