The Circle
Constructor Tool
The circle constructor tool is used to construct
a circle based on previously defined geometric objects. In this way it
differs from the circle tool available in the Create Panel. There are
three
ways to construct a circle: by two points, by a point and a
segment,
and by three points. The following diagrams show these three
possibilities.
In each diagram there is a before and after view - the objects on the
left
are the objects that must be selected to create the circle on the
right.
In the first example, we select points 1
and 2 and then click on the circle constructor tool to create a circle
on these two points.

In the second example, we select
point
1 and segment 2 (in that order) and then click on the circle
constructor
tool to create a circle on with center at point 1 and radius equal to
the
segment's length.

In the third example, we select point
three
points and then click on the circle constructor tool to create the
unique
circle that passes through these three points. (Note: This last
construction
depends on the parallel postulate and thus is not available in
Hyperbolic or Elliptic Geometry)