We draw a pair of perpendicular lines intersecting at a point 0, called the origin.
One of the lines, the x-axis. is usually taken in a horizontal position.
The other line, the y-axis, is then taken in a vertical position.
The x and y-axes together arc called coordinate axes (Figure 4.1), and they form a rectangular coordinate system, or a Cartesian (after Rene Descartes) coordinate system.
We now choose a point