Solve the Problem $\mathrm { f } ( \theta ) = \cos \theta$

Multiple Choice

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

A) $- \frac { 3 } { 4 }$
B) $\frac { 3 } { 4 }$
C) $\frac { 1 } { 4 }$
D) $- \frac { 1 } { 4 }$