Diameter of a Circle Formula

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The diameter is the line passing through the center of a circle touching the two points on the edge of the circle. The diameter is also called a chord. A chord is defined as a line which joins any two points on the edge of a circle. The diameter is a chord which crosses from the center point of a circle. Therefore, diameter is the longest possible chord i.e. line in a circle. In other words, diameter of a circle is a line segment passing through the center of the circle and whose end points lie on the circle.

The diameter of a circle can be calculated in the following ways:

Method 1:  When the radius is known
Radius is a line segment from the center of the circle to the edge of the circle. Therefore, when radius of a circle is given the diameter is calculated by:
 D = 2r, Where r = radius of a circle

Method 2: When the circumference is known
Circumference is the distance around the circle. Therefore, when the circumference is known diameter can be calculated as follows:
D = C/π, Where C = circumference of the circle
π = pie, approximately equal to 3.14

Method 3: When the area of the circle is given
When the area of the circle is given, then the diameter of the circle can be calculated by following:
D = √(4A/π), Where A = area of the circle
π = pie, equal to 3.14

 
Problem 1: Calculate the diameter of the circle:

a.      Radius = 5cms
b.      Circumference = 96cms

Solution: A. Radius = 5cms
=> Therefore, diameter of the circle is calculated as follows: D = 2r
= 2*5 = 10cms

B. Circumference = 96cms
=> Therefore, the diameter can be calculated as follows: D = C/π
= 96/3.14 = 30.57 cms
 

Problem 2: Calculate the diameter of the circle if Area = 180 cms.
Solution: Given Area = 180cms

=> Therefore, the diameter can be calculated as follows: D = √4A/π
= √4*180/3.14 = 15.14 cms

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