title: Finding coordinates of a point between two points?
body: <p>Doing some 3D stuff in wpf- want to use a simpler test to see if everything is working (before moving to curves).</p>
  
  <p>The basic question is given two points x1,y1,z1 and x2,y2,z2 I have calculated the distance between the points.  But how to find the coordinates of another point (x3,y3,z3) that lies on that line at some distance?</p>
  
  <p>I.e. if my line is 100 long between -50,0,0 and 50,0,0 what are the coordinates of the point at 100 * 0.1 along the line? </p>
  
  <p>I think this is a simple formula but I haven't found it yet....</p>