Tools for Constructions

We have previously used rulers and protractors to measure segments and angles, and sometimes to draw geometric figures.  In these lessons you will learn how to draw accurate geometric figures using only a straight-edge and a compass.  A ruler is a straight-edge, but you will not need the units in most cases.

A straight-edge is used to construct a line (or a segment) that contains two given points.  That one and only one such line exists is one of the postulates of Euclidean geometry.

A compass is used to draw a circle when given two points, one being its center and the other being a point on its circumference.  By definition, a circle is the set of all points equidistant from the center.

You will need a compass and straight-edge for the homework with these lessons.  Any simple ruler will do as a straight-edge, and an inexpensive compass, such as that shown below, will work fine.

There is a website (the link is given at the bottom of each page containing a construction) that uses java programs to animate all of the constructions we will consider, so if you have trouble understanding any of them, please go to that link.

Further information on constructions can be found here.  

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