9.
已知\(f\left( \alpha \right)=\dfrac{\tan (-\alpha -\pi ){{\sin }^{2}}(-\alpha -\pi )}{\sin (\alpha -\dfrac{\pi }{2})\cos (\dfrac{\pi }{2}+\alpha )\tan (\pi -\alpha )}\).
\((1)\)化简\(f\left( \alpha \right)\);
\((2)\)若\(f\left( \alpha \right)=2\),求\(\dfrac{3\sin \alpha +\cos \alpha }{2\sin \alpha -\cos \alpha }\)的值.