# What is a coordinate system? Definition and example

A rectangular coordinate system refers to two number lines that intersect at right angles. The figure below shows the coordinate system.

Notice how the horizontal line or blue line is called x-axis and the vertical line or red line is called y-axis.

Because the x-axis and the y-axis lie on a plane, we can also call the coordinate system a coordinate plane.

## Why do we need a rectangular coordinate system?

The main purpose of a coordinate system is to locate points. Once you know how to locate points, you could also use the coordinate plane to graph lines, quadratic equations, and so forth ...

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