求值：

\((1)\sin 50{}^\circ (1+\sqrt{3}\sin 10{}^\circ )\)

\((2)\dfrac{2{{\cos }^{2}}42{}^\circ +\sin 75{}^\circ \cos 81{}^\circ -1}{\cos 6{}^\circ -\cos 75{}^\circ \cos 81{}^\circ }\)