# Trigonometry

## What Is Trigonometry?

Trigonometry is a branch of mathematics that studies the angles and lengths of the sides of triangles. Trigonometry particularly deals with functions which relate the angle of a right triangle with the lengths of its sides: the sine function, cosine function and tangent function.## Dictionary Definition

The Oxford English Dictionary defines trigonometry as "that branch of mathematics which deals with the measurement of the sides and angles of triangles, particularly with certain functions of their angles or of angles in general (the sine, cosine and tangent)."## Where Does the Word Trigonometry Come From?

Trigonometry comes from the Greek words 'trigonon' ("triangle") and 'metron' ("measure").## The Curriculum

The lessons are grouped into mini-curriculum to help you organise your learning. A brief description is given for each mini-curriculum. Click the**MORE**button to learn more.

## Right Triangle

Right triangles (in American English) or right-angled triangles (in English English) are triangles containing one angle of 90° (called a right angle).
In this mini-curriculum, you will learn about right triangles and their sides.

## Pythagoras' Theorem

Pythagoras' theorem concerns the relationship between the lengths of the three sides of a right triangle.
In this mini-curriculum, you will learn about Pythagoras' theorem and how to use it.

## Sine Function

The sine function is a trigonometric function. The sine of the angle in a right triangle is equal to the ratio of the length of the opposite side to the length of the hypotenuse.
In this mini-curriculum, you will learn about the sine function and how it can be used to find angles and lengths of sides in a right triangle.

## Cosine Function

The cosine function is a trigonometric function. The cosine of the angle in a right triangle is equal to the ratio of the length of the adjacent side to the length of the hypotenuse.
In this mini-curriculum, you will learn about the cosine function and how it can be used to find angles and lengths of sides in a right triangle.

## Tangent Function

The tangent function is a trigonometric function. The tangent of the angle in a right triangle is equal to the ratio of the length of the opposite side to the length of the adjacent side.
In this mini-curriculum, you will learn about the tangent function and how it can be used to find angles and lengths of sides in a right triangle.

## Area of a Triangle Using Trigonometry

Even though trigonometry mostly concerns right triangles, it can be used for any triangle.
In this mini-curriculum, you will learn about finding the area of a triangle using trigonometry.