Constructions with a single straightedge

Constructions with a single straightedge are geometric constructions where you are only allowed to use a straightedge (an unmarked ruler) to draw straight lines. Unlike classical constructions, you do not use a compass to draw circles or measure distances. Some constructions are possible with just a straightedge, especially if a circle is already given.

Important properties

• You can draw a straight line through any two given points.

• You cannot transfer distances or draw circles without a compass.

• If a circle is given, you can use its properties (like finding tangents or diameters) with just the straightedge.

• Some constructions possible with compass and straightedge are impossible with only a straightedge.