Product Identities Formula

Equation for calculate product identities is,

Product Identities Equations:
sinθ.cosφ = [ sin(θ+φ) + sin(θ-φ) ] / 2
cosφ.cosφ = [ cos(θ+φ) + cos(θ-φ) ] / 2
sinθ.sinθ = [ cos(θ+φ) - cos(θ-φ) ] / 2