Q20Long answer
Prove that for all n ∈ N cos α + cos (α + β) + cos (α + 2β) + ... + cos (α + (n – 1) β) n −1 nβ cos α + β sin 2 2 = β 2 sin 2n θ
Prove that for all n ∈ N cos α + cos (α + β) + cos (α + 2β) + ... + cos (α + (n – 1) β) n −1 nβ cos α + β sin 2 2 = β 2 sin 2n θ