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.
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