Goal: Find the area of a circle.

You need to know:

• Pi is approximately 3.14.
• To "square" a number means to multiply it by itself.
• Remember order of operations! Exponents first!

The formula for finding the area (A) of a circle:

Remember that r = radius. The radius is the distance from the edge of a circle to its center. It is half of the diameter.

Example 1:

Find the area of this circle.

Solution

A = 3.14 x 3 squared
A = 3.14 x 9
A = 3 28.26 square feet

Example 2:

Find the area of the shaded region.

Solution

Step 1: Find the area of the circle. Since we are given the diameter, we divide it in half to get the radius.

A = 3.14 x 12 squared
A = 3.14 x 144
A = 452.16 square inches

Step 2: Find the area of the square.

A = 24 x 24
A = 576 square inches

Step 3: Subtract.

A = 576 - 452.16
A = 123.84 square inches

You try it:

Find the area of a circle that has a radius of 6 feet.

Click here for the answer.