A crucial concept basic to the study of trigonometry is the idea of an "angle". Without a good understanding of the basic geometrical meaning of angles and angular measure, developing a good understanding of trigonometry is essentially impossible. In this chapter, in order to provide a review of this topic for students who may benefit from such a review, we discuss the basic ideas of angles and angular measure, and review the common units (degrees or radians) used to specify angles, i.e. directions in the plane. We also explain why it is that the same physical direction in the plane can correspond to more than one value of the angle describing it.
We begin by providing some physical motivation for why we might want to specify directions in the plane using numbers (angles) in the first place, and then discuss the basic conventions that allow us to do any of the following:
LINKS FOR CHAPTER 1 TOPICS:
Click on the link for the appropriate topic below for more information on that topic. In general, it would be a good idea to go through the material in the order listed, unless you are returning to this page for a refresher on a particular topic (or topics).