created 08/26/97; revised 08/14/00; 07/26/03

We have used the dot product in several calculations:

**Length:**Dot product of vector with itself = length^{2}**Perpendicularity:**Dot product of perpendicular vectors = 0**Angle:**cos θ = dot product of two unit vectors

This chapter adds nothing new, but extends the third application to the angle between vectors in 3D space.