定义\(2×2\)矩阵\(f\left( x \right)=\left[ \begin{matrix} \cos x-\sin x & \sqrt{3} \\ \cos \left( \dfrac{\pi }{2}+2x \right) & \cos x+\sin x \\\end{matrix} \right]\) ，若\(\left[ \begin{matrix} a{}_{1} & {{a}_{2}} \\ {{a}_{3}} & {{a}_{4}} \\\end{matrix} \right]={{a}_{1}}{{a}_{4}}-{{a}_{2}}{{a}_{3}}\)，则\(f\left( x \right)=(\) \()\)