A circle is the collection of all points in a plane that are equidistant from a fixed point in the plane.

The fixed point is called the center of the circle.

**Circumference: **The perimeter of a circle is called Circumference. See fig.(c).

**Circumference = π × Diameter**

**Circumference = 2 × π × Radius**

** Radius:** The distance from the center to a point on the circle is called the radius of the circle. Radius denoted by r. See fig.(a).

**Diameter: **A chord of a circle passing through its center is called a diameter of the circle. Diameter is the longest chord of a circle. It is denoted by D. See fig.(b).

note, diameter is always twice the Radius. **Diameter formula is here**:

**Diameter = 2 × Radius**

## Radius, Diameter and Circumference

## Area

### What is the area of circle?

The area of circle is multiplication of π and the the squared of radius, which is written as:

**A = π r ^{2}**

where,

- A is the area
- r is the radius of the circle
- The value of
**π is equal to 3.14 or 22/7**

**Example: What is the area of a circle with radius of 10.5 m ?**

As we know, Area = πr2

= π × 10.5^{2}

= 3.14 × (10.5 × 10.5)

= 346.18 (to 2 decimals)

Or if we know **Diameter** then,

**Area of circle = (π/4) × D ^{2}**