If `hati+hatj+hatk,2hati+5hatj,3hati+2hatj-3hatk` and `hati-6hatj-hatk` are the position vectors of points A, B, C and D respectively, then find the angle between `vec(AB)` and `vec(CD)`. Deduce that `vec(AB)` and `vec(CD)` are collinear.

Answer

Since `0le theta le pi`, it follows that `theta=pi`. This show that `vec(AB)` and `vec(CD)` are collinear.