Circumference
Areas of plane figures
 
The length of the circumference, the value of  the number π.

How many times is the length of a circumference larger than its diameter?
 
Take the blue dot to the right in order to see the circumference of the circle spread.
Check to how many diameters it is equivalent, you can move them  from their centre.
The number π expresses the relation between the circunference of a circle and  its diameter.

We use a Greek letter π called Pi to write it.
The number π is not a natural or rational number because it has infinite number of decimal digits.
π = 3.141592654.....
We usually use two decimal digits and we say π = 3.14

The formula for the circunference of a circle is:
circumference = π · diameter
l = π · d
Taking the radius as a reference:
circunference = 2 · π · radius
l = 2 · π · r
       
           
  Eduardo Barbero Corral
 
Spanish Ministry of Education , Social Afairs and Sport. Year 2007
 
 

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