Let cos a b )= 4 5 July 8, 2019 16 32 64 128 Let a 6 b 3 and cos ab )= 4 5 Cos 0 + cos 45 + sin 30 into sin 90 - cos 45 + cos 60 Cosa=1 3 cos(a+b)=-1 3 求a b∈(0 p 2)求cos(a-b)
