Circles – Properties of Plane Shapes

A circle is a simple closed shape. It is the set of all points in a plane that are at a given distance from a given point. The centre: equivalently, it is the curve traced out by a point that moves in a plane.

Area of a circle = \( \scriptsize \pi r^2 \)

Area of a semi circle = \( \frac {1}{2} \scriptsize \pi r^2\)

• The circumference is the distance around the circle.

• A radius (Plural radii) is any straight line joining the centre of the circle to any point on the circumference.

• A diameter is a straight line joining two points on the circumference and passing through the centre of the circle. The diameter divides a circle into two equal parts. Each part is called a semicircle.

• An arc is a part of the circumference of a circle.

• A chord is a straight line joining two points on the circumference.

• A segment is a region between a chord and the circumference.

• A sector is a region between two radii and the circumference.