Circle

A circle is a type of line. Imagine a straight line segment that is bent around until it's ends join. Then arrange that loop until it is exactly circular - that is, all points along that line are the same distance from a center point.

A circle is the set of points in a plane that are equidistant from a given point O. The point O is called the center and the distance r from the center to any point on the circle is called the radius, and. Twice the radius is known as the diameter d=2r.

Center: A point inside the circle. All points on the circle are equidistant (same distance) from the center point.

Radius: The radius is the distance from the center to any point on the circle. It is half the diameter.

Diameter: The line segment whose endpoints belong to the circle and passes through the center.

Lines and Line Segments Related to Circles

Chord: a segment whose endpoints lie on a circle.

Secant: line that contains a chord.

Tangent: line in the plane of a circle that intersects the circle at exactly one point.

Point of Tangency: the point of intersection between a circle and a tangent to the circle.