2．
\((1)\)设函数\(f(x)=\begin{cases} & x+1,x\leqslant 0, \\ & {{2}^{x}},x > 0, \\ \end{cases}\)且，则\(f(f(-\dfrac{1}{2}))=\) ．
\((2)\)设扇形的半径长为\(2cm\)，面积为\(4c{{m}^{2}}\)，则扇形圆心角的弧度数是 \((\)圆心角为正角\()\)．
\((3)\overrightarrow{a}\)，\(\overrightarrow{b}\)的夹角为\(120^{\circ}\)，\(|\overrightarrow{a} |=1\)，\(|\overrightarrow{b} |=3\)，则\(|5\overrightarrow{a}-\overrightarrow{b} |=\)________．
\((4)\)已知\(f\left( x \right)={{x}^{3}}+\left( a-1 \right){{x}^{2}}\)是奇函数，则不等式\(f\left( ax \right) > f\left( a-x \right)\)的解集是 ．