The Art of Circles

The Radius is a line segment from the center to the circumference   $R\ =\ D\div2$  

The Diameter is a line segment from circumference to circumference passing through the center of the circle  $D\ =\ 2\times R$   

The circumference is the perimeter of a circle

To find the measurement of circumference we can...

 $C=d\pi$    or    $C=2\pi r$  

The number $\pi$  is a mathematical constant. It is defined as the ratio of a circle's circumference to its diameter. 

 $\pi$  is approximately 3.14  in numerical value. 

We could estimate  $\pi$  as 3