2. THE AREA OF A CIRCLE
An introduction to approximating the area of a circle.

3. PLAN – Use areas we already know
We know the area of squares.
Approximate the area of a circle
by finding the area of squares:
One inside the circle.
One outside the circle.

4. Dimensions of the Circle and Squares

5. What is the area…
of this big square?

6. What is the area…
of this big square?
Area = 2r x 2r
= 4r2

7. What is the area…
of the circle?
Circle Area <
4r2

8. What is the area…
of the small square?

9. What is the area… of the small square? Think… What other shapes is the
small square made of?

10. What is the area… of the small square? Area = 2 x Triangle Area
= 2 x ½ x 2r x r
= 2r2

11. Small Square Area < Circle Area < Big Square Area
What is the area…
of the circle?
Small Square Area < Circle Area < Big Square Area
2r2
< Circle Area <
4r2