^2-y^2}{x^2+y^2}$ has a
  limit at the origin, the previous problem suggests that limit
  will be $-3/5$.</p>

  <div class="problem">
    Please read the previous example. Recall that we are looking
    for the limit of the function $\ds
    f(x,y)=\frac{x^2-y^2}{x^2+y^2}$ at the origin (0,0).

    <div class="marginpar">
      You may want to look at a graph in <a href=
      "https://sagecell.sagemath.org/?z=eJxL06jQqdS01aiIM9KtjDPS1AextEEsXq7k_LyS_NKi-IKc_BKNNB2gSl1jHWNNHY1KKCM5Pye_KCmxyDakqDRVJzk3scBWP