Convert the Expression into a Product $\cos \frac { 3 \pi } { 8 } - \sin \frac { \pi } { 8 }$

Multiple Choice

Convert the expression into a product. Simplify where possible. $\cos \frac { 3 \pi } { 8 } - \sin \frac { \pi } { 8 }$ (Hint: Use the identity $\cos \theta = \sin \left( \frac { \pi } { 2 } - \theta \right)$ .)

A) $\frac { \sqrt { 2 } } { 2 }$
B) 1/2
C) 1
D) 0
E) $\frac { \sqrt { 3 } } { 2 }$