Given that \[\cos x = \frac{5}{{13}}\]for \[{270^ \circ } < x < {360^ \circ }\], find \[\sin \left( {\frac{1}{2}x} \right)\]. Express your answer in simplified radical form.
\[\frac{{2\sqrt {13} }}{{13}}\]
300
Transform \[\sin (4x)\tan (2x)\] into an expression that utilizes only \[\sin (x)\] and \[\cos (x)\] and does not contain a denominator.
\[8{\sin ^2}(x){\cos ^2}(x)\]
300
Rewrite the expression, filling in the blank:
\[\sin ( - {80^ \circ }) = \_\_\_\_\_\_\_({10^ \circ })\]