已知函数\(f(x)=\begin{cases} & {{x}^{2}}+x,\ \,\,\,-2\leqslant x\leqslant c, \\ & \dfrac{1}{x},\quad \ \ \ \ \ \,\,c < x\leqslant 3. \end{cases}\) 若\(c=0\)，则\(f(x)\)的值域是____；若\(f(x)\)的值域是\([-\dfrac{1}{4},2]\)，则实数\(c\)的取值范围是____．