已知函数\(f(x)= \sqrt{3}\cos (2x- \dfrac{π}{3})-2\sin x\cos x \)．

\((I)\)\(f\)\((\)\(x\)\()\)的最小正周期；

\((II)\)求证：当\(x∈[- \dfrac{π}{4}, \dfrac{π}{4}] \)时，\(f(x)\geqslant - \dfrac{1}{2} \)．