**What is the coordinate system?**

A coordinate system, or more precisely, a Cartesian coordinate system, is a method to precisely present the position of points, whether on a plane (two-dimensional) or in three-dimensional space. In this chapter, we will focus on a coordinate system on a plane, that is, a system made up of two axes (straight lines) that are perpendicular to each other (forming a 90-degree angle between them).

To facilitate the understanding of the material, let's look at the following drawing, which gives an example of a two-dimensional coordinate system:

As mentioned, as can be seen in the drawing, it is customary to identify the horizontal axis with **$X$** and the vertical axis with **$Y$**.

The intersection point between the two axes is called the **origin** and is usually identified with the letter **$O$**.

Along the **$X$**** horizontal axis**, the numbers increase to the right of the origin and decrease to the left of the origin.

Along the **$Y$**** vertical axis**, the numbers increase upwards in relation to the origin and decrease downwards in relation to the origin.