已知函数\( \overrightarrow {a}=(2\sin x,\sin x-\cos x), \overrightarrow {b}=( \sqrt {3}\cos x,\cos x+\sin x),f(x)= \overrightarrow {a}\cdot \overrightarrow {b}\)．
\((1)\)求\(f(x)\)的最小正周期及\(f(x)\)在区间\([0, \dfrac {π}{2}]\)上的最大值和最小值；
\((2)\)若\(f(x_{0})= \dfrac {6}{5},x_{0}∈[ \dfrac {π}{4}, \dfrac {π}{2}]\)，求\(\cos 2x _{0}\)的值．