Khan Academy: Linear Algebra: Defining the Angle Between Vectors

Video uses the vector triangle inequality and the law of cosines to demonstrate and prove the definition of the angle between vectors. Uses the definition of the angle between vectors to define perpendicular vectors. Shows that the dot product of perpendicular vectors is 0 and extends to define orthogonal vectors. Illustrates the distinction between the meaning of perpendicular and orthogonal. [25:11]