# cosine

/kˈəʊsaɪn/ (UK) · CEFR C1 · Noun

Source: https://englishreference.com/word/cosine
Updated: 2026-05-31

## Definition

a mathematical value used to find the lengths and angles of triangles. It compares the side next to an angle with the longest side of a right-angled triangle.

For teachers: the ratio of the side adjacent to a given angle to the hypotenuse in a right-angled triangle. It is a fundamental trigonometric function that oscillates between -1 and 1.

## Examples

- You need to calculate the cosine of the angle to find the distance.
- In the physics lab, students used the cosine of the launch angle to determine the horizontal component of the projectile's velocity.
- The wave's amplitude is modeled using a cosine function, which accurately represents the periodic nature of the oscillation over a specific time interval.

## Usage notes

- Often abbreviated as 'cos' in mathematical notation and formulas.

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