title: compute a vector which is perpendicular to another given vector (all are in 3D)
body: <p>I have a vector <code>v1</code> (suppose <code>v1= a1,b2,c1</code>) and this <code>v1</code> passes through the point <code>x1,y1,z1</code>. Now I need a second vector, <code>v2</code> which is perpendicular to the <code>v1</code>. Suppose that <code>v2</code> is passing through the second point <code>x2,y2,z2</code>.  </p>
  
  <p>However, my final goal is to find the intersection point of above two lines. So, could you help me to find the vector which is perpendicular to another given vector?  PLZ Anyone helps me.</p>