1. Area of a Circle
Mrs. Cronnelly

2. Why don’t we have just one formula for area?
Why is it that the area of a square or a rectangle is base x height but the area of a circle is A =  r²?
Wouldn’t it make sense to have just
one formula for area?
Well actually, we do!
It is base x height!

3. Here is a step by step process to help us see this more clearly!
If we cut a pie that has
A diameter of 9 inches into
eight slices and arrange
them into a parallelogram
Like this!
9 in

4. We now have a parallelogram!
height
4.5 in r
base in
A = b x h
A = x 4.5
A = in²
How close are we?
A =  r²
A = 3.14 x 4.5²
A = in²

7. Let’s see how well you can find the Circumference of a circle!

8. (Round to the nearest tenth)
C= 12.6 cm
C= 72.2 mm
C= 56.5 m
C= cm

9. Now let’s practice how to find the area of a circle!

10. (Round to the nearest tenth)
A= m²
A= 10,563 cm²
A= 12.6 cm²
A= mm²

11. Mix it up!!!!! A = 210.665 cm² 52.82 cm Area Distance around
(two halves make a whole circle)
Area
Distance around
Find the area
of the circle
Find Circumference of a circle
A= cm²
40.82 cm
Find the area
of a rectangle
Find Perimeter
of rectangle
(be careful!)
A = 78 cm²
12 cm
A = cm²
52.82 cm

12. Radius = 3.8 cm Diameter =7.6 cm Area = 45.3 cm²
(Round to the nearest tenth)
Radius = 3.8 cm
Diameter =7.6 cm
Area = 45.3 cm²

13. Radius = 3.5 ft Area = 38.465 ft² Diameter = 7 ft
(Round to the nearest tenth)
Radius = 3.5 ft
Area =
ft²
Diameter = 7 ft
Circumference = ft