title: Find the angle between two vectors from an arbitrary origin
body: <p>I would like to know how to get the angle on the picture when the origin is not O(0,0,0), but (a, b, c) where a, b, and c are variables.</p>
  
  <p>B is a point that makes 90 degrees with A(d, e, f) and the origin.</p>
  
  <p>The image is here:</p>
  
  <p><img src="https://i.imgur.com/eTDM6wX.jpg" alt="screenshot"></p>