2.
\((1)\)已知幂函数\(y\)\(=\)\(f\)\((\)\(x\)\()\)的图像经过点\(\left(\begin{matrix}2, \dfrac{ \sqrt{2}}{2}\end{matrix}\right)\),则\(f\)\((4)\)的值为______
\((2)\)函数\(y={{\log }_{\frac{1}{2}}}({{x}^{2}}-4x-5)\)的递减区间为______
\((3)\)方程\(\left(\begin{matrix} \dfrac{1}{2}\end{matrix}\right)\) \({\,\!}^{x}\)\(=3-\)\(x\)\({\,\!}^{2}\)的实数解的个数是________.
\((4)\)关于\(x\)的不等式\(|x-1|+|x-2|\leqslant a^{2}+a+1\)的解集为空集,则实数\(a\)的取值范围是 ____.