About Circles

A circle, geometrically, is a simple closed shape. More specifically, it is a set of all points in a plane that are equidistant from a given point, called the center. It can also be defined as a curve traced by a point where the distance from a given point remains constant as the point moves.

Parts of a circle

• Center (or origin): the point within a circle that is equidistant from all other points on the circle.
• Radius: the distance between any point on the circle and the center of the circle. It is equal to half the length of the diameter.
• Diameter: the largest distance between any two points on a circle; by this definition, the diameter of the circle will always pass through the center of the circle. It is equal to twice the length of the radius.
• Circumference: the distance around the circle, or the length of a circuit along the circle.
• Arc: part of the circumference of a circle
• Chord: a line segment from one point of a circle to another point. A chord that passes through the center of the circle is a diameter of the circle.
• Sector: the area of a circle created between two radii.

The constant π

The radius, diameter, and circumference of a circle are all related through the mathematical constant π, or pi, which is the ratio of a circle's circumference to its diameter. The value of π is approximately 3.14159. π is an irrational number meaning that it cannot be expressed exactly as a fraction (though it is often approximated as 7 over 22) and its decimal representation never ends or has a permanent repeating pattern.