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
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 r2
- 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 × 10.52
area of a circle= 3.14 × (10.5 × 10.5)
= 346.18 (to 2 decimals)
Or if we know Diameter then,
Area of circle = (π/4) × D2