bmatrix}(3t^2)' \\ (2/t)'\end{bmatrix}
        dt=\begin{bmatrix}\blank{1in}\\\blank{1in}\end{bmatrix}dt.$$
        If we are at $t=2$, then our differential becomes $d\vec r
        = \begin{bmatrix}\blank{1cm}\\\blank{1cm}\end{bmatrix}$. If
        we move to $t=2.1$, then the change in $t$ is $\Delta
        t=\blank{1cm}$ and the change in $\vec r$, as estimated by
        the differential $d\vec r$ at $t=2$, is approximately
        $\Delta \vec r\approx
        \begin{bmatrix}\blank{1cm}\\\blank{1cm}\