title: how to plot ellipse given a general equation in R?
body: <p>Ellipse general equation:</p>
  
  <pre><code>a * x ^ 2 + b * y ^ 2 + c * x * y + d * x + e * y + f = 0
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/sHAEt.png" rel="noreferrer"><img src="https://i.stack.imgur.com/sHAEt.png" alt="enter image description here"></a></p>