# Cosine of an Angle

## Cosine of an Angle

Algebraic measure of the orthogonal projection on one of the sides of an angle of measure θ of a unit vector carried by the other side of the angle.

$$\cos{(\textit{θ})}\space = \space \frac{x}{1}\space = \space x$$

When we associate with any real number the cosine of the angle whose measure, in the circular system, is this number, we thereby define a circular function called a cosine function.

### Notation

The cosine of the angle x is noted as cos(x) and is read as “cos of x” or “cosine of angle x“.

### Example

Graphic representation of the function f(x)= cos(x) with amplitude 1 and period 2π.