9.
设向量 \( \overrightarrow{m}=(\sin x,-1)\),\( \overrightarrow{n}=( \sqrt {3}\cos x,- \dfrac {1}{2})\),函数\(f(x)=(\) \( \overrightarrow{m}+ \overrightarrow{n})⋅ \overrightarrow{m}.\)
\((1)\)求函数\(f(x)\)的单调递增区间;
\((2)\)当\(x∈(0, \dfrac {π}{2})\)时,求函数\(f(x)\)的值域.