title: what is the inverse function of Sinc
body: <p>I've searching the whole day to calculate the inverse function of <code>sinc(x) </code> between <code>-pi  and pi </code>, but couldn't find anything:</p>
  <p><img src="https://i.stack.imgur.com/SktCj.png" alt="enter image description here" /></p>
  <p>Does anybody know a way to get the angle value from the a given <code>sinc</code> value ?  If it make easier I'm only interested in the area between <code>-pi and pi </code>
  Thanks in advance for any help.</p>