Circle
A circle is the set of points in a plane that are equidistant from a given center point.
Circle is an elementary-school-level concept. It is listed in the California State Standards for Grade 1.
Examples
| Unit Circle: | The unit circle is a circle of radius one. |
Prerequisites
| Diameter: | (1) In plane geometry, the diameter is the straight-line distance between two points opposite one another across the center of a circle. (2) In solid geometry, the diameter is the straight-line distance between two antipodal points on a sphere. |
| Radius: | The radius of a circle is the distance from its center to its circumference or from the center of a sphere to its surface. The radius is equal to half the diameter. |