Coordinates in the Plane
To represent points in the plane, two perpendicular straight lines are used. They are called the Cartesian axes or coordinate axes.
The horizontal axis is called the x-axis.
The vertical axis is called the y-axis.
Point O, where the two axes intersect is called the origin.
The coordinates of a point, P, are represented by (x, y).
The distance measured along the horizontal axis is the x-coordinate or the abscissa.
The distance measured along the vertical axis is the y-coordinate or the ordinate.
Plotting Points
The coordinate axes divide the plane into four equal parts called quadrants.
Signs
| Quadrant | Abscissa | Ordinate |
|---|---|---|
| I | + | + |
| II | − | + |
| III | − | − |
| IV | + | − |
The origin, O, has coordinates (0,0).
The points that are on the vertical axis have their abscissa equal to 0.
The points that are on the horizontal axis have their ordinate equal to 0.
The points in the same horizontal line (parallel to the x-axis) have the same ordinate.
The points in the same vertical line (parallel to the y-axis) have the same abscissa.
Exercise
Plot the following points:
A(1, 4), B(-3, 2), C(0, 5), D(-4, -4), E(-5, 0), F(4, -3), G(4, 0), H(0, -2)
