8.
已知点\(A\),\(B\),\(C\)的坐标分别为\(A(3,0)\),\(B(0,3)\),\(C(\cos α,\sin α)\),\(α∈( \dfrac {π}{2}, \dfrac {3π}{2}).\)
\((1)\)若\(| \overrightarrow{AC}|=| \overrightarrow{BC}|\),求角\(α\)的值;
\((2)\)若\( \overrightarrow{AC}⋅ \overrightarrow{BC}=-1\),求\( \dfrac {2\sin ^{2}α+\sin 2α}{1+\tan \alpha }\)的值.