Solve the Equation $$\cos ( 2 \theta ) = \frac { \sqrt { 2 } } { 2 }$$

Solve the equation. Give a general formula for all the solutions.
- $$\cos ( 2 \theta ) = \frac { \sqrt { 2 } } { 2 }$$

A) $\theta = \frac { \pi } { 8 } + 2 \mathrm { k } \pi , \theta = \frac { 7 \pi } { 8 } + 2 \mathrm { k } \pi$
B) $\theta = \frac { 2 \pi } { 3 } + \mathrm { k } \pi , \theta = \frac { 4 \pi } { 3 } + \mathrm { k } \pi$
C) $\theta = \frac { \pi } { 4 } + \mathrm { k } \pi , \theta = \frac { 3 \pi } { 4 } + \mathrm { k } \pi$
D) $\theta = \frac { \pi } { 8 } + \mathrm { k } \pi , \theta = \frac { 7 \pi } { 8 } + \mathrm { k } \pi$