In basic trigonometry, it is used to determine unknown side lengths or an acute angle measurement(s). In more advanced mathematics, cosine is treated simply as a function without an apparent or direct reference to a triangle (the triangle's presence becomes assumed). Examples of this may be seen in Calculus through the process of integration. Wherein, the function cosine may only be a part of a large equation.
Cosine is one component out of a three-part acronym known as: SOHCAHTOA. The term cosine occupies the "CAH," wherein the series forms: Cosine (equals) Adjacent (over) Hypotenuse.
Cosine thus represents the ratio of the Adjacent side length to the Hypotenuse side length -- this is all in relation to an (acute) angle, theta.
When dealing with an angle measurement, x ("theta"), the side "touching" the angle is referred to as the Adjacent side; the side furthest away from the angle is referred to as the Opposite side; and, in a right triangle, the hypotenuse always remains and, simplistically, may be recognized as the diagonal side.
In mathematical procedures, cosine is abbreviated as "cos" for convenience.
Note: UrbanDictionary entries do not support Entity, Hex or Decimal browser rendering. This definition replaces the Greek small letter, "theta", with an "x."
However, in reality, it appears as an "o" or a "zero" with a line going horizontally through the center.
2. Sine / Cosine = Tangent
3. 'the integral of' 2x cos(3x) dx