# Double-angle's cosine( related to the cosine and the sine)

## Description

rigonometric identities are equalities that involve trigonometric functions and are true for every single value of the occurring variables. Geometrically, these are identities involving certain functions of one or more angles.

The sine of an angle is defined in the context of a right triangle, as the ratio of the length of the side that is opposite to the angle divided by the length of the longest side of the triangle (the hypotenuse ).

The cosine of an angle is also defined in the context of a right triangle, as the ratio of the length of the side the angle is in divided by the length of the longest side of the triangle (the hypotenuse ).

The tangent (tan) of an angle is the ratio of the sine to the cosine.

The cosine of the double-angle can be calculated by the sine and cosine of the single-angle.

## Variables

ω | Double-angle ( ω=2θ ) (radians) |

θ | Single angle (radians) |