Line (Coordinate Geometry)

Definition: A geometrical object that is straight, infinitely long and infinitely thin. Its location is defined by two or more points on the line whose coordinates are known.
Try this Adjust the line below by dragging an orange dot at point A or B and see how the line AB behaves. You can also drag the origin point at (0,0).

A location of a line on the coordinate plane is defined by two or more points whose coordinates are known. The line passes through both points and goes on forever in both directions. It has no endpoints.

This is the same as the definition of a line in ordinary plane geometry, the only difference being that we know the coordinates of the points involved. The naming conventions are also the same.

Things to try

  1. In the above diagram, press 'Reset'. The line AB passes through point A at (52,7), point B at (53,20) and goes to infinity in both directions.
  2. Drag A, B or the origin point and construct various other lines to get a feel for the concept.

See also the Definition of a Line in plane geometry.


In the interest of clarity in the applet above, the coordinates are rounded off to integers and the lengths rounded to one decimal place. This can cause calculatioons to be slightly off.

For more see Teaching Notes

Other Coordinate Geometry topics