marginpar">
          Use <a href=
          "http://sagecell.sagemath.org/?z=eJwL0SjSKclILUnUtNUo0krOL9aA8HQUirSKM_OgPE1eLl6ugqLMvBIFpZCMVIWU1KLMssSSzLJUhcxiJZBkiF5KZlqahibcOADvtxuX&amp;lang=sage">
          Sage</a> to check your work.
        </div> Compute the partial derivatives $\ds\frac{\partial
        \vec T}{\partial r}$ and $\ds\frac{\partial \vec
        r}{\partial \theta}$, and then state the derivative $D\vec
        T(r,\theta)$. [Hint: $D\vec T$ is a 2 by 2 matrix, and each
        partial 