title: How to find where an equation equals zero
body: <p>Say I have a function and I find the second derivative like so: </p>
  
  <pre><code>xyr &lt;- D(expression(14252/(1+exp((-1/274.5315)*(x-893)))), 'x')
  
  D2 &lt;- D(xyr, 'x')
  </code></pre>
  
  <p>it gives me back as, typeof 'language': </p>
  
  <pre><code>-(14252 * (exp((-1/274.5315) * (x - 893)) * (-1/274.5315) * (-1/274.5315))/(1 + 
      exp((-1/274.5315) * (x - 893)))^2 - 14252 * (exp((-1/274.5315) * 
      (x - 893)) * (-1/274.5315)) * (2 * (exp((-1/274.5315) * (x - 
      893)) * (-1/274.5315) * (1 + exp((-1/274.5315) * (x - 893)))))/((1 + 
      exp((-1/274.5315) * (x - 893)))^2)^2)
  </code></pre>
  
  <p>how do I find where this is equal to 0?</p>