Solve the Problem $f ( \theta ) = \cos \theta$ And $f ( a ) = - \frac { 1 } { 12 }$

Multiple Choice

Solve the problem.
-If $f ( \theta ) = \cos \theta$ and $f ( a ) = - \frac { 1 } { 12 }$ , find the exact value of $f ( a ) + f ( a - 2 \pi ) + f ( a + 4 \pi )$ .

A) $- 36$
B) $- 12$
C) $- \frac { 1 } { 12 }$
D) $- \frac { 1 } { 4 }$