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如图,在平面直角坐标系\(xOy\)中,点\(P\)是圆\(O\):\(x^{2}+y^{2}=1\)与\(x\)轴正半轴的交点,半径\(OA\)在\(x\)轴的上方,现将半径\(OA\)绕原点\(O\)逆时针旋转\( \dfrac {π}{3}\)得到半径\(OB.\)设\(∠POA=x(0 < x < π)\),\(f(x)=( \overrightarrow{OA}+ \overrightarrow{OB})\cdot \overrightarrow{OP}\).
\((1)\)若\(x= \dfrac {π}{2}\),求点\(B\)的坐标;
\((2)\)求函数\(f(x)\)的最小值,并求此时\(x\)的值.