1. The problem statement, all variables and given/known data Given 2 lines, determine whether they are intersecting or not. If they are, determine the angle between them. Line(1): x = 1-t, y = 3-2t, z = t Line(2): x = 2+3t, y = 3+2t, z = 1+t 2. Relevant equations cos(theta) = (a·b)/([itex]\left|a\right|[/itex][itex]\left|b\right|[/itex]) 3. The attempt at a solution I know that they intersect, I've done all the work in my notebook and checked the back of the book for the answer and they indeed intersect. My problem lies with finding the angle. Since I have those two lines up above, doesn't that mean I can find the direction vectors of both and both direction vectors will intersect with the same angle as the lines? If so, I tried using the above equation with a = <-1,-2,1> and b=<3,2,1> and I am unable to get 49.1° which is the answer.