If $$\sin A = {3 \over 5}$$, where $$450^\circ < A < 540^\circ $$, then $$\cos {A \over 2}$$ is equal to

What is $${1 \over {\sin 10^\circ }} - {{\sqrt 3 } \over {\cos 10^\circ }}$$ equal to?

The maximum value of $$\sin \left( {x + {\pi \over 6}} \right) + \cos \left( {x + {\pi \over 6}} \right)$$ in the interval $$\left( {0,{\pi \over 2}} \right)$$ is attained at

If $$K = \sin \left( {{\pi \over {18}}} \right)\sin \left( {{{5\pi } \over {18}}} \right)\sin \left( {{{7\pi } \over {18}}} \right)$$, then what is the value of K?