h;80 for more
      practice.</span>
    </div>Complete the following:

    <ol>
      <li>Let $f(x,y)=3xy^3+e^{x}.$ Compute the four second
      partials $$\ds \frac{\partial^2 f}{ \partial x^2},\quad
      \ds\frac{\partial^2 f}{\partial y \partial x},\quad
      \ds\frac{\partial^2 f}{\partial y^2}, \quad \text{ and
      }\ds\frac{\partial^2 f}{\partial x \partial y}.$$</li>

      <li>For $f(x,y)=x^2\sin(y)+y^3$, compute both $f_{xy}$ and
      $f_{yx}$.</li>

      <li>Make a conjecture about a relat