# Definition:Trigonometry

## Definition

**Trigonometry** is the branch of mathematics which studies the relationships between the lengths of sides and angles of triangles.

### Spherical Trigonometry

**Spherical trigonometry** is the branch of mathematics which concerns the measurement of spherical triangles and related figures on the surface of a sphere.

## Also see

- Results about
**trigonometry**can be found**here**.

## Historical Note

The field of **trigonometry** emerged in ancient Greece during the $3$rd century BCE from applications of geometry to astronomical studies.

While the Greeks focused on the calculation of chords, mathematicians in India created the earliest-known tables of values for trigonometric functions such as sine.

An analytic approach to **trigonometry** was introduced by Leonhard Paul Euler.

## Linguistic Note

The word **trigonometry** derives from the Greek **trigōnon** (**triangle**) and **metron** (**measure**), literally meaning **measurement of triangles**.

## Sources

- 1977: Gary Chartrand:
*Introductory Graph Theory*... (previous) ... (next): Chapter $1$: Mathematical Models: $\S 1.2$: Mathematical Models - 2008: Ian Stewart:
*Taming the Infinite*... (previous) ... (next): Chapter $5$: Eternal Triangles - 2014: Christopher Clapham and James Nicholson:
*The Concise Oxford Dictionary of Mathematics*(5th ed.) ... (previous) ... (next):**trigonometry**