
如图,点\(P _{0}\)是锐角\(α\)的终边与单位圆的交点,\(OP _{0}\)逆时针旋转\( \dfrac {π}{3}\)得\(OP _{1}\),\(OP _{1}\)逆时针旋转\( \dfrac {π}{3}\)得\(OP _{2}\),\(…\),\(OP _{n-1}\)逆时针旋转\( \dfrac {π}{3}\)得\(OP _{n}\).
\((1)\)若\(P _{0}\)的坐标为\(( \dfrac {3}{5}, \dfrac {4}{5})\),求点\(P _{1}\)的横坐标;
\((2)\)若点\(P _{2020}\)的横坐标为\( \dfrac {4}{5}\),求\(\sin (2α+ \dfrac {2π}{3})\)的值.