# cosine

## English

English Wikipedia has an article on:
Wikipedia

### Etymology

co- +‎ sine, short for complementi sinus in Latin, meaning “sine of the complement”.

### Pronunciation

• (UK) enPR: kō'sīn, IPA(key): /ˈkəʊ.saɪn/
• (US) enPR: kō'sīn, IPA(key): /ˈkoʊ.saɪn/
•  Audio (UK) (file)

### Noun

cosine (plural cosines)

1. (trigonometry) In a right triangle, the ratio of the length of the side adjacent to an acute angle to the length of the hypotenuse. Symbol: cos

#### Usage notes

In various branches of mathematics, the cosine of an angle is determined in various ways, including the following:

• The x-coordinate of the point on the unit circle at the given anticlockwise angle from the x-axis.
• The sum of the real or complex power series

$\sum _{n=0}^{\infty }{\frac {(-1)^{n}x^{2n}}{(2n)!}}=1-{x^{2} \over 2}+{x^{4} \over 24}-{x^{6} \over 720}+{x^{8} \over 40320}-\cdots$

cosine f

## Old French

### Noun

cosine f (oblique plural cosines, nominative singular cosine, nominative plural cosines)

1. (female) cousin

#### Descendants

• French: cousine