Cosine dictionary definition

cosine

[kō′sīn′]

noun

the reciprocal of the secant; specif.

the ratio of the adjacent side of a given acute angle in a right triangle to the hypotenuse
an equivalent, positive or negative ratio for certain related angles (Ex.: the cosine of 57° or 303° is .5446, of 123° or 237° is -.5446) or real numbers representing radians (Ex.: cosine of .9948 radians (57°) is .5446)

Origin of cosine

Modern Latin ; from co. sinus, short for complementi sinus, literally , sine of the complement

noun

Abbr. cos

In a right triangle, the ratio of the length of the side adjacent to an acute angle to the length of the hypotenuse.
The abscissa at the endpoint of an arc of a unit circle centered at the origin of a Cartesian coordinate system, the arc being of length x and measured counterclockwise from the point (1, 0) if x is positive or clockwise if x is negative.

cosine

cos &thgr; = bc

Noun

(plural cosines)

(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 where x is in radians.

Related terms

Anagrams

Cosine function

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

See sine.