title: Why Math.Atan(Math.Tan(x)) != x?
body: <p>If tan(x) = y and atan(y) = x why Math.Atan(Math.Tan(x)) != x?</p>
  
  <p>I´m trying to calculate x in something like: </p>
  
  <pre><code>tan(2/x +3) = 5 
  </code></pre>
  
  <p>so </p>
  
  <pre><code>atan(tan(2/x + 3) = atan(5)
  </code></pre>
  
  <p>and so on... but I´ve tried this: </p>
  
  <pre><code>double d = Math.Atan(Math.Tan(10));
  </code></pre>
  
  <p>and d != 10. Why?</p>