title: finding a point away from d distance orthogonaly from a given 3D line
body: <blockquote>
    <p>I want to find the coordinate of a point (say P) which is away from a known distance (say d). 
    the case is: I want the point that lie on a line (3d) which is perpendicular to the another given 
    line segment (3d) and passing through the one end of that given line segment (say A). 
    So, I know 2 end points (also vector along the line) of the given line segment and distance d and vector of the perpendicular line.  Also point C where the perpendicular line pass through is also 
    known.
    I am having <code>vector3</code> class and line3 class. </p>
  </blockquote>
  
  <p>the method to tackle this problem is difficult to figure out, so please help me in this regard by showing the way.</p>
  
  <p>Yes, as there are 2 points on that line in opposit direction, I am looking for the point (P), which is closer to point C (not the Q).</p>
  
  <p>thank you in advance</p>
  
  <p><img src="https://i.stack.imgur.com/4IHHr.jpg" alt="enter image description here"></p>