Lines and circles are the important elementary figures in geometry. We know that a line is a locus of a point moving in a constant direction, whereas the circle is a locus of a point moving at a constant distance from some fixed point. The theoretical importance of the circle is reflected in the number of amazing applications. Here we will discuss the properties of a circle, area and circumference of a circle in detail.
The collection of all the points in a plane, which are at a fixed distance from a fixed point in the plane, is called a circle. Here, the fixed point is called the centre “O”. Some of the important terminologies used in the circle are as follows:
| Terms | Description |
| Circumference | The boundary of the circle is known as the circumference |
| Radius | The line from the centre “O” of the circle to the circumference of the circle is called the radius and it is denoted by “R” or “r” |
| Diameter | The line that passes through the centre of the circle and touches the two points on the circumference is called the diameter and it is denoted by the symbol “D” or “d” |
| Arc | Arc is the part of the circumference where the largest arc is called the major arc and the smaller one is called the minor arc |
| Sector | Sector is slice of a circle bounded by two radii and the included arc of a circle |
| Chord | The straight line that joins any two points on the circumference of a circle is called the chord |
| Tangent | A line that touches the circumference of a circle at a point is called the tangent |
| Secant | A line that cuts the circle at the two distinct points is known as the secant |
Some of the important properties of the circle are as follows:
Area of a circle, A = πr 2 square units
The circumference of a circle = 2πr units
The circumference of a circle formula can also be written as πd.
Diameter = 2 x Radius
Here “r” represents the radius of a circle.
