Find the Exact Value of the Expression $\sin 135 ^ { \circ } - \sin 270 ^ { \circ }$

Multiple Choice

Find the exact value of the expression. Do not use a calculator.
- $\sin 135 ^ { \circ } - \sin 270 ^ { \circ }$

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