Sine and cosine - Wikipedia
The sine and cosine functions, along with other trigonometric functions, are widely available across programming languages and platforms. In computing, they are typically abbreviated to sin and cos.

Sine, Cosine and Tangent - Math is Fun
Sine, Cosine and Tangent are the main functions used in Trigonometry and are based on a Right-Angled Triangle. Before getting stuck into the functions, it helps to give a name to each side of a right triangle: Opposite is always opposite the angle. And Adjacent is always next to the angle.

Cosine | Definition, Formulas, & Facts | Britannica
The cosine is a fundamental trigonometric function such that the cosine of an angle of a right triangle is the ratio of its adjacent side to the hypotenuse.

Sine, Cosine, Tangent, explained and with Examples and practice ...
This page explains the sine, cosine, tangent ratio, gives on an overview of their range of values and provides practice problems on identifying the sides that are opposite and adjacent to a given angle.

Cosine Function in Math - Definition, Formula, Examples
Learn about the cosine function in math. Get its definition, formula, and examples in trigonometry, geometry, and calculus.

Trigonometric functions - Wikipedia
The trigonometric functions most commonly used in modern mathematics are the sine, the cosine, and the tangent functions. Their reciprocals are respectively the cosecant, the secant, and the cotangent functions, which are less commonly used.

COSINE Definition & Meaning - Merriam-Webster
The meaning of COSINE is a trigonometric function that for an acute angle is the ratio between the leg adjacent to the angle when it is considered part of a right triangle and the hypotenuse.

Cosine - Math.net
Cosine, written as cos⁡ (θ), is one of the six fundamental trigonometric functions. There are two main ways in which trigonometric functions are typically discussed: in terms of right triangles and in terms of the unit circle.

Trigonometric Identities - Math is Fun
They are just the length of one side divided by another. For a right triangle with an angle θ : When we divide Sine by Cosine we get: So we can say: That's our first Trigonometric Identity. We can also divide "the other way around" (such as Adjacent/Opposite instead of Opposite/Adjacent) to get: sin (θ) = 2/4, and csc (θ) = 4/2.

Cosine -- from Wolfram MathWorld
The cosine function cosx is one of the basic functions encountered in trigonometry (the others being the cosecant, cotangent, secant, sine, and tangent). Let theta be an angle measured counterclockwise from the x-axis along the arc of the unit circle.