Geometric Constructions
Geometric figures that are created with
only a compass and straightedge are called
geometric constructions. Since the Golden
Age of Greece, people have made a game of
geometric constructions. Over the centuries,
people have enjoyed using their compass and
straightedge, to discover just what they
could and could not construct. In this lesson
you will get your chance to play the game of
geometric construction.
Neither a ruler nor a protractor is ever used to create geometric constructions. Rulers
and protractors are measuring tools, not construction tools. (You may use a ruler as a
straightedge in constructions provided you do not use its marks for measuring.)
Construction Tips
1. You begin a construction by selecting a starting point. From that point you usually make a line
(or ray or segment) with your straightedge, or a circle (or arc) with your compass. A line used
to begin a construction is often referred to as a construction line.
2. Once your construction is underway, you generally position your construction tools using
clearly identified points. These are usually points where two lines, two circles, or a circle and
a line intersect.
3. Don’t erase your construction marks (segments, arcs, circles) when you finish a construction.
Your construction marks show your method. They are the footprints that allow someone to
track your progress. In a construction, the method of construction is as important as the
finished product.
4. For a complicated construction, make a sketch before starting. Then label it. This may help
clarify your task.