title: Inverse of math.atan2?
body: <p>What is the inverse of the function </p>
  
  <pre><code>math.atan2
  </code></pre>
  
  <p>I use this in Lua where I can get the inverse of <code>math.atan</code> by <code>math.tan</code>.<br>
  But I am lost here.</p>
  
  <p><strong>EDIT</strong></p>
  
  <p>OK, let me give you more details.</p>
  
  <p>I needed to calculate angle between 2 points (x1,y1) and (x2,y2) and I did,</p>
  
  <pre><code>local dy = y1-y2 
  local dx = x1-x2
  local angle = atan2(dy,dx)* 180 / pi
  </code></pre>
  
  <p>Now if I have the angle, is it possible to get back dy and dx?</p>