cosine

Cosine (or cos) is a trigonometric function that gives the ratio between two specific sides of a right-angled triangle.

In a right-angled triangle, one angle is 90° and the other two angles are acute angles.

Label one of the acute angles θ.

The cosine of this angle is the ratio between the length of the adjacent side and the length of the hypotenuse (the side opposite the right angle).

The function, therefore, is:

    Cos θ = adjacent \div hypotenuse