AREA OF A CIRCLE

In the figure at the right, which

lines are radii of the circle?

You can see that this circle is

divided into square sections. If you

will look closely, you will see that

the circumference passes through some

fraction of the smaller squares.

Count the small squares in one

quarter of the circle. If you

estimate the fraction of a unit, you

should get a total close to _78_.

To find the area of the complete circle, multiply 78 x 4 = _312_.

You have estimated that there are about 312 squares in the circle.

The radius of this circle is equal to _______________ units.

(how many?)

The formula for the area of a circle is:

A = π r2 (This is r x r.)

If r = 10, then A = π 102 (102 = 10 x 10)

A = 3.14 x 100

A = 314 square units

Your estimated answer was 312, which is very close to the actual number.

Remember, area is always expressed in square units.

Now, try this one:

What is the area of a circle if the radius = 8 feet?

A = π r2

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