Let us recall the fundamentals of circles which we studied in previous chapters.
A closed line consisting of all points on the plane that are equidistant from a given point on the plane is called a circle.
Diameter of the circle:
  • The distance across the circle.
  • The length of any chord (a straight line which connects two points on a circle) passing through the center.
  • It is twice the radius.
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Diameter \(=\) \(2 ×\) Radius \(=\) \(2r\) 
Radius of the circle:
The radius is the distance from the center to any point on the circle.
Radius is also known as half of the diameter.
Area of the circle:
The area of a circle is the number of square units inside that circle.
Area of the circle \(=\) πr2 sq. units
Here \(r\) is the radius of the circle.
The value of the π [pi] can be either \(22/7\) or \(3.14\).