A complex cosine

$\large \dfrac { \cos { \left( \dfrac { \pi }{ 504 } \right) } +\cos { \left( \dfrac { \pi }{ 1008 } \right) } }{ \cos { \left( \dfrac { \pi }{ 672 } \right) } } = x + \dfrac1x$

Let $x$ a complex number different from zero satisfying the equation above, such that $\left| x \right| =1$ . The option that correctly express the value of ${ x }^{ 2016 }$ is...