created: 08/26/97; revised: 08/14/00, 07/26/03, 07/23/09, 01/18/15, 04/02/16

The dot product is used for:

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

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

What is the angle between two edges of a cardboard box that meet in a corner?