If \(\cos \alpha,\cos\beta, \cos \gamma\) are direction cosines of any straight line, then

\(cos 2 \alpha+\cos 2 \beta+\cos 2 \gamma=1\) \(cos 2 \alpha+\cos 2 \beta+\cos 2 \gamma=2\) \(cos 2 \alpha+\cos 2 \beta+\cos 2 \gamma=-2\) \(cos 2 \alpha+\cos 2 \beta+\cos 2 \gamma=-1\)

\(cos 2 \alpha+\cos 2 \beta+\cos 2 \gamma=-1\)

\(\cos (2\alpha)+\cos (2\beta)+\cos (2\gamma)=2\left(\cos^2 \alpha+\cos^2 \beta+\cos^2 \gamma \right)-3\)