• ### Domain

The set of all possible inputs of a function.

• ### Function

An operation that assigns a correspondence from elements of one set to elements of another set.

• ### Period

The repeating interval of a periodic function; the period of a function is a real number.

• ### Periodic Function

A function that repeats itself in regular intervals; it follows this equation: f (x + c) = f (x), where c is a constant.

• ### Range

The set of all possible outputs of a function.

• ### Reference Angle

The positive acute angle formed between the terminal side of an angle and the x-axis.

• ### Rule

The part of a function that dictates the exact correspondence between the elements of one set and the elements of another set.

• ### Trigonometric Functions

There are six trigonometric functions: Sine, cosine, tangent, cosecant, secant, and cotangent.

• ### Unit Circle

The circle whose center is at the origin and whose radius is one.

• ### Formulae

 Cosecant Given a point P(x, y) on the terminal side of an angle θ in standard position, distance d from the origin, cosecant(θ) = csc(θ) = . Cosine Given a point P(x, y) on the terminal side of an angle θ in standard position, distance d from the origin, cosine(θ) = cos(θ) = . Cotangent Given a point P(x, y) on the terminal side of an angle θ in standard position, cotangent(θ) = cot(θ) = . Secant Given a point P(x, y) on the terminal side of an angle θ in standard position, distance d from the origin, secant(θ) = sec(θ) = . Sine Given a point P(x, y) on the terminal side of an angle θ in standard position, distance d from the origin, sine(θ) = sin(θ) = . Tangent Given a point P(x, y) on the terminal side of an angle θ in standard position, tangent(θ) = tan(θ) = . 