**Introduction:** A

circle is all points equidistant from one

point called the

center of the circle. Segments drawn near and through the

circle create other geometrical objects which we define.

**The Lesson:** We show circle O below. A circle is named based on the name of the point which is the center. The segment OA is a radius of the circle.

**Definition:** A

radius is the

segment connecting (sometimes referred to as the “distance between”) the center and the

circle itself.

In the diagram below, we show circle O with radius OA.

Segments and lines of interest are:

**Definitions:**- diameter: the segment connecting two points of the circle and containing the center
- chord: any segment with endpoints on the circle
- tangent: any segment, which if extended in either direction, will only intersect the circle once
- secant: a segment or line which passes through a circle, intersecting at two points

In the diagram below, we show circle O.

Angles of interest are:

**Definitions:**