Using a Sum or Difference Identity, Write the Following as an Expression

Multiple Choice

Using a sum or difference identity, write the following as an expression involving functions of x.
- $\sin \left( x - \frac { \pi } { 2 } \right)$

A) $\frac { \sqrt { 2 } } { 2 } \cos x - \frac { \sqrt { 2 } } { 2 } \sin x$
B) $\frac { \sqrt { 2 } } { 2 } \cos x + \frac { \sqrt { 2 } } { 2 } \sin x$
C) $- \cos x$
D) $\sin x$