Let $a,b\in\mathbb{R}$, $(a\neq 0)$. If the function $f$ defined as $f(x)= \begin{cases} \dfrac{2x^{2}}{a}, & 0\le x<1 \\ a, & 1\le x<\sqrt{2} \\ \dfrac{2b^{2}-4b}{x^{3}}, & \sqrt{2}\le x<\infty \end{cases}$ is continuous in the interval $[0,\infty)$, then an ordered pair $(a,b)$ is :