7th Grade Math - Circles Lesson
Circumference and Area of a Circle
The diameter of a circle is the distance from one point on the circle to another point on the circle, through its center.
The radius of a circle is the distance from its center to a point on the circle.
The length of a circle's radius is half the length of its diameter.
The circumference of a circle is the distance around the circle.
Pi () is a non-repeating, non-terminating decimal which is equivalent to the ratio of a circle's circumference to its diameter. 3.14 is often used as an approximation of pi.
Circumference = d or 2r
Area = r2