# Area of a Circle

A circle is the set of all points in a plane at a given distance (called the radius) from a given point (called the center.)

A line segment connecting two points on the circle and going through the center is called a diameter of the circle.

Clearly, if d represents the length of a diameter and r represents the length of a radius, then d = 2r.

The circumference C of a circle is the distance around the outside. For any circle, this length is related to the radius r by the equation

C = 2πr

where π (pronounced "pi") is an irrational constant approximately equal to 3.14.

The area of a circle is given the formula

A = πr2.

Example:

What is the area of a circular table with diameter 6 ft?

Given that, the diameter of the circular table is 6 ft.

So, the radius of the circular table is half of the diameter. That is, radius is 3 ft.

Use the formula for area of a circle, A = πr2 , where r is the radius of the circle.

Substitute 3 for r in the formula.

Therefore, the area of the circular table is about 28.27 ft 2