Prove that cos 4 5 cos 12 13 cos 33 65 July 8, 2019 16 32 64 128 Prove that cos 1 4 5 )+ cos 1 12 13 )= cos 1 33 65 Cosa=1 3 cos(a+b)=-1 3 求a b∈(0 p 2)求cos(a-b) Cos 0 + cos 45 + sin 30 into sin 90 - cos 45 + cos 60 Cos 1 cos 2 cos 3
