hi everyone

Assume that $\displaystyle \alpha ,\beta ,\gamma$ satisfy $\displaystyle 0< \alpha < \beta < \gamma < 2\pi $ if,

$\displaystyle \cos(x+\alpha )+\cos(x+\beta )+\cos(x+\gamma )=0,\forall x \in \mathbb{R}$.

$\displaystyle \gamma -\alpha $Find

just hints

thanks.