Circumference: C=2pir
C stands for circumference. pi is 3.14... and r is the radius.
of course, you can always do, C=pid. where d is diameter because the radius is half the diameter
Area: A=pir^2
A stands for the Area, pi stands for 3.14... r stands for radius, and the little ^2 is the equation squared. The way to solve that is square the radius and then multiply what you got from squaring the radius by pi.
DO NOT replace radius with the diameter when trying to find the Area
