The charge flowing in a conductor changes with time as Q(t)=α t-β t^2+γ t^3. Where α, β and γ are constants. Minimum value of current is:

The charge flowing in a conductor changes with time as $\displaystyle Q(t)=\alpha t-\beta t^2+\gamma t^3$. Where $\displaystyle \alpha, \beta$ and $\displaystyle \gamma$ are constants. Minimum value of current is :