# @Cos (Formula Language)

Given an angle in radians, returns the cosine of the angle. In a right triangle, the cosine of an acute angle is the ratio of the length of its adjacent side to the length of the hypotenuse.

@Cos( angle )

## Parameters

angle

Number or number list. An angle measured in radians.

## Return value

cosine

Number or number list. The cosine of angle, from -1 to 1.

## Usage

If the parameter is a list, the function operates on each element of the list, and the return value is a list with the same number of elements.

## Examples

1. This formula returns 1.
``@Cos( 2 * @Pi )``
2. This formula returns 1 and -1 in a list.
``@Cos( (2 * @Pi) : @Pi )``
3. This formula finds the length of side c in triangle ABC. You know the value of angle C in radians, and the lengths of sides a and b. This formula finds the length of side c.
``````@Sqrt( @Power( sideA; 2 )+@Power( sideB; 2 )-
( 2*sideA*sideB*( @Cos( angleC ) ) ))``````

This formula is a version of the law of cosines, which states that for any triangle ABC, c2 = a2+b2-2ab(cos(C)).