Geometry construction using a compass and straightedge

Given three points, it is always possible to draw a circle that passes through all three. This page shows how to construct (draw) a circle through 3 given points with compass and straightedge or ruler. It works by joining two pairs of points to create two
chords.
The perpendicular bisectors
of a chords always passes through the center of the circle. By this method we find the center and can then draw the circle.

* Note
Depending where the center point lies on the bisector, there is an infinite number of circles that can satisfy this.
Two of them are shown on the right.
Steps 2 and 4 work together to reduce the possible number to just one.

Try it yourself

Click here for a printable worksheet containing two problems that use this construction technique.
When you get to the page, use the browser print command to print as many as you wish. The printed output is not copyright.