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Question Number 140114 by EnterUsername last updated on 04/May/21
If cos α+cos β+cos γ=0=sin α+sin β+sin γ, then  (A) cos(2α)+cos(2β)+cos(2γ)=0  (B) sin(3α)+sin(3β)+sin(3γ)=3sin(α+β+γ)  (C) cos(3α)+cos(3β)+cos(3γ)=3cos(α+β+γ)  (D) sin(2α)+sin(2β)+sin(2γ)=0
$$\mathrm{If}\:\mathrm{cos}\:\alpha+\mathrm{cos}\:\beta+\mathrm{cos}\:\gamma=\mathrm{0}=\mathrm{sin}\:\alpha+\mathrm{sin}\:\beta+\mathrm{sin}\:\gamma,\:\mathrm{then} \\ $$$$\left(\mathrm{A}\right)\:\mathrm{cos}\left(\mathrm{2}\alpha\right)+\mathrm{cos}\left(\mathrm{2}\beta\right)+\mathrm{cos}\left(\mathrm{2}\gamma\right)=\mathrm{0} \\ $$$$\left(\mathrm{B}\right)\:\mathrm{sin}\left(\mathrm{3}\alpha\right)+\mathrm{sin}\left(\mathrm{3}\beta\right)+\mathrm{sin}\left(\mathrm{3}\gamma\right)=\mathrm{3sin}\left(\alpha+\beta+\gamma\right) \\ $$$$\left(\mathrm{C}\right)\:\mathrm{cos}\left(\mathrm{3}\alpha\right)+\mathrm{cos}\left(\mathrm{3}\beta\right)+\mathrm{cos}\left(\mathrm{3}\gamma\right)=\mathrm{3cos}\left(\alpha+\beta+\gamma\right) \\ $$$$\left(\mathrm{D}\right)\:\mathrm{sin}\left(\mathrm{2}\alpha\right)+\mathrm{sin}\left(\mathrm{2}\beta\right)+\mathrm{sin}\left(\mathrm{2}\gamma\right)=\mathrm{0} \\ $$

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