Circles

What's the deal?

Special Vocabulary

circle = a closed shape with all of the points the same distance from the center


radius = the distance from the center to the outside of the circle


diameter = the distance across the circle, going through the center; 2 radii


circumference = a special work for the perimeter of the circle

What is pi??

Pi is a special number. Pi is found in every single circle in the world. It's the ratio of the circumference to the diameter.


In other words, if you measure the circumference of ANY circle and divide it by the diameter of that circle, you'll always get pi!


We use 3.14 to represent pi because it's easier to work with.

Area

The formula for finding the area of a circle is pi x r x r which just means 3.14 x radius x radius. You need to know how long the radius is, then you just "plug in" the number and do the math.

Circumference

There are two ways to find the circumference:

pi x diameter OR (3.14 x diameter)

pi x radius x 2 (3.14 x radius x 2)