Finding the perimeter of shapes that have corners are easy. All you need to do is to add all the sides and you are good to go! But in the case of a shape that doesn't have a corner, things are different. Take a look at a circle. It doesn't have a corner then how do we find the perimeter of a circle? That is why, in this resource, we will discuss the perimeter of a circle and its calculation.
What is a Circle's Perimeter?
Put a point on the length of a circle. Take a whole loop and when you reach that point, stop your loop. That is the perimeter of a circle. Basically, the perimeter of a circle is the length around a circle. Mathematicians gave it a special name of a circle's perimeter, they call it circumference. Some people also call it the boundary of a circle. Don't mix it with the area of a circle, the area of a circle means the space occupied inside of a circle, while the circumference is the measurement of the length of a circle. In nutshell, the circumference is the length around a circle, that is to say, it is the perimeter of the circle.
In ancient times, mathematicians use to cut the circle and make it a straight line to find the perimeter of the circle. In 240 B.C, Archimedes, Greece mathematician, came up with the concept of 
. He found a way to find the perimeter of a circle. Today, we all use that concept to find the circumference of a circle. It is not 
accurate but accurate enough to work with.
The above formula can be used to find the circumference of a circle. All you need is the diameter of a circle to find the circumference. If you are given the radius, no need to worry, the radius is half of the diameter, use this concept to solve your problem.
Examples and Problems
If the circumference of a circle is 
, what is its area?
Calculate the circumference of a wheel with a diameter of 
.
Calculate the area of the square inscribed in a circle with a circumference of 
.
By applying the Pythagorean theorem for one of the triangles, we obtain:
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I’m just curious if the area between the polygon and the circumscribed circle has a name.
https://www.superprof.co.uk/resources/academic/maths/geometry/plane/orthocenter-centroid-circumcenter-and-incenter-of-a-triangle.html