Objects > Circles

Circles are fundamental objects in Euclidean geometry. In classical geometric constructions, you use a compass to construct circles.

A circle is a path object.

Sketchpad provides several different ways to construct a circle.

Use the Compass tool to construct a circle using a center point and another point which defines the radius.
Use the Construct \| Circle by Center+Point command to construct a circle using a center point and another point which defines the radius.
Use the Construct \| Circle by Center+Radius command to construct a circle using a center point and either a segment or a distance measurement to define the radius.

•	Construct a point on a circle using the Point tool or the Construct \| Point on Object command. Then animate the point around the circle or use the point as the driver for a locus.

•	Attach an independent point to the circle by using the Edit \| Merge command.

•	Use Construct \| Interior to construct the interior of a circle.

•	Use Construct \| Intersection to construct a circle’s intersection with a straight object, another circle, an arc, a point locus, or a function plot.

•	Use Graph \| Define Unit Circle to define a coordinate system that uses the selected circle as its unit circle.

Use the Measure menu to find:

•	the Circumference of a circle

•	the Radius of a circle

•	the Area of a circle

•	the Equation of a circle