   intersect/angle
  How do we determine if two vectors intersect, and if they do then how do we determine the angle of there intersection provided that the z unit vector is our reference vector? Thank you. 
  All vectors intersect at the origin.  Do you mean line segments or rays?What problem are you trying to model? ;  This is why i gotta read some more, but okay line segments, and on the side, how is a ray different from a vector?;  A vector indicates a direction only.  A line/ray has a vector to indicate its direction and a point that it passes through in space to indicate its location.There are four possibilities:1) two lines intersect each other in all points (i.e. they are the same line)2) two lines do not ever intersect each other and are parallel3) two lines intersect each other in exactly one point4) two lines do not ever intersect each other and are not parallel (called skew lines)Since a line is one-dimensional, a line can be represented in parameter form (parameter t) where each value of t defines a point on the line.  If you know the direction vector of the line, VA and a point on the line A0, then the equation of the line is:  Line AA(t) = A0 + t*VA  Line BB(t) = B0 + t*VBFirst, check if the direction vectors are the same (i.e. is VA just a scalar multiple of VB?).  If so, then it''s either scenario 1 or 2.  Then, you just need to see if point A0 is on Line B (does any single value of t solve Line B''s 3 equations?).  If it is, then it''s scenario 1, otherwise scenario 2.Here''s where my memory gave way and my laziness kicked in...a good reference for you is: http://mathforum.org/library/drmath/view/62814.html;  Hey, help is help. Thank you for yours. ;  If you have a point with a vector in the form,x   ady=  b   + ez   cfit can then be solved simultaneously with the other vector to see if they intercept.If they do to get the angle from vectors:d  he  if  jd*h+e*i+f*j=((d*e*f)^(1/2)) * ((h*i*f)^(1/2)) *cos(angle)This will give the angle between the two vector one you have found they intercept. ;  Argh non-standard size font set the top bit is xyz = abc + def in line etc. 