sinαsinβ=-[cos(α+β)-cos(α-β)]

cosαcosβ=[cos(α+β)+cos(α-β)]

sinαcosβ=[sin(α+β)+sin(α-β)]

cosαsinβ=[sin(α+β)-sin(α-β)]

2. Sum-difference product formula

sinθ+sinφ=2sincos

Sinθ-sinφ= 2 cosine

cosθ+cosφ=2coscos

cosθ-cosφ=-2 sin