# Circles

Navigation: Objects > # Circles |

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Circles are fundamental objects in Euclidean geometry. In classical geometric constructions, you use a compass to construct circles. A circle is a path object. You can change the object properties, label properties, and display attributes of circles. |

| Construct a Circle

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. |

| Use a Circle

• | 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.

| Measure a 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