In three dimensional geometry, if a line makes angles $\alpha ,\beta \mathrm{and}\gamma$ with coordinates axes, then which of the following is true?

If $\cos \alpha ,\cos \beta \text{and }\cos \gamma$ are the DC’s of a line, then $2{\cos }^2\alpha +2{\cos }^2\beta +2{\cos }^2\gamma =2$

$\Rightarrow 1+\cos 2\alpha +1+\cos 2\beta +1+\cos 2\gamma =2\Rightarrow \cos 2\alpha +\cos 2\beta +\cos 2\gamma +1=0$