1) If a=cos2α+isin2α,b=cos2β+isin2β,c=cos2γ+isin2γ and d=cos2δ+isin2δ then √abcd+1√abcd= A) √2cos(α+β+γ+δ) B) 2cos(α+β+γ+δ) C) cos(α+β+γ+δ) D) none of these Answer: Option BExplanation: we have, abcd=cos(2α+2β+2γ+2δ)+isin(2α+2β+2γ+2δ) √abcd=cos(α+β+γ+δ)+isin(α+β+γ+δ) ..(i) ∴ 1√abcd=cos(α+β+γ+δ)−isin(α+β+γ+δ) ....(ii) Adding (i) and (ii) , we obtain √abcd+1√abcd=2cos(α+β+γ+δ)