Formulas for Circumference and Area of a Circle, with Examples
These videos use π and the approximation 3.14 for π in computing the circumference and area of a circle. Students must already know how to work with decimals.
π is an irrational number, which means it CANNOT be written as a terminating decimal (like 3.14) or a fraction (like 22/7). Both 3.14 and 22/7 are only approximations.
π is defined as the ration of the circumference of a circle to its radius. Click this link for a cool video someone else made showing why π is close to 22/7.
Circles 1: http://www.youtube.com/watch?v=62ZzBhZINZU
Circles 2: http://www.youtube.com/watch?v=NWbTrbJlWCg