How to find the area of a circle

How do you find the area of a circle?

Before we find the area, there are a few parts of the circle we should know about. So here's a brief anatomy lesson of a circle.

It is the same distance from the center to any point on the circle. This distance has a special name. It is called the radius.

If I combine two radii (just the fancy plural name for more than one radius), it also give me my diameter.

Note, the diameter is the same as 2 x the radius, or 2 x radius equals your diameter.

Now that we know are essential circle parts, we have a special recipe that gives us the area of a circle.

The recipe is:  

The "r" in the formula is the length of your radius.
π is apprx 3.14. Depending on what your teacher prefers, you can sometimes leave answers in terms of π, or multiply it using your calculator.

Tip: Many calculators have a π button.

So let's try to find the area of the following circle (and yes, it happens to be a pizza!):

So for the above pizza, we know it has a radius (there's that word again!) of 8 inches. In other words, we know the distance from the center of the circle to the edge is 8 inches.
So how do we find the area?

We use the recipe!

Area = 

Area of the pizza = π x (8)²

                          = π x 64 or 64π
                          = 64 x 3.14
                          = 200.96 in²

The area of the pizza is 200.96 square inches. 

How can we take it further?

You could have been given the diameter, in which case you would have to divide it in two to plug in the "r" into the recipe.

Or, perhaps you were told what the area is, and asked to find the length of the radius. 

See upcoming blogs for these scenarios...including how to find the area of just one pizza slice!