title: Reverse calculation of sqrt()
body: <p>I'm making a online RPG game where I use this math formula (found online) to calc exp -> level.</p>
  
  <pre><code>$level = (25 + sqrt(625 + 100 * $exp)) / 50;
  </code></pre>
  
  <p>I have tried for days to make a script to reverse it.
  My goal is to make a function to calc the amount of exp required for a level.</p>