Find the Exact Value of the Expression If θ = $f ( \theta ) = \cos \theta \quad$

Multiple Choice

Find the exact value of the expression if θ = 45°. Do not use a calculator.
- $f ( \theta ) = \cos \theta \quad$ Find $f ( \theta )$

A) $\frac { \sqrt { 3 } } { 3 }$
B) $\sqrt { 2 }$
C) $\frac { \sqrt { 2 } } { 2 }$
D) $- \frac { \sqrt { 2 } } { 2 }$