This chapter sets up standards for dealing with angles. Not only are they used for rotation, but they're also used to establish direction for vectors. This chapter also defines the trigonometric functions, which are used whenever you want to model wavelike oscillating motion or model a scenario with a right triangle. They are also used extensively in Chapter 4, “Vector Operations,” when we discuss vectors. The last two sections focus on identities for manipulating trig functions within equations and using the trig functions in C++. This chapter lays the groundwork for all the chapters that follow.