Perimeter and Area- Circles

Key Concepts

Circles are 2D shapes characterised by all points on the shape being equidistant from a central point, also known as the circle’s centre.
Diameter refers to the line passing through the centre of a circle, touching two points on its perimeter.
Radius is a line that connects the centre of the circle to any point on its perimeter. It is half the length of the diameter.
The circumference is the perimeter of the circle, i.e., the total distance around its edge.
The area of a circle is the total space enclosed within its perimeter.

The diameter (d) of a circle is twice the radius (r): d = 2r
The circumference (C) of a circle is obtained using the formula: C = πd or C = 2πr
The area (A) of a circle is calculated using the formula: A = πr²

To calculate the radius from the diameter, divide the diameter by 2.
To calculate the diameter from the radius, multiply the radius by 2.
To calculate the circumference, multiply the diameter by π, or multiply the radius by 2π.
To calculate the area, square the radius and then multiply by π.

Calculating the length of a fence around a circular garden requires finding the circumference of the garden.
Determining the amount of paint needed for a circular area will need calculation of the circle’s area.
In real world, circles appear in multiple instances from clock faces to traffic signs and wheels. Any calculation involving these shapes will require the understanding of the above concepts.