2. CIRCLES

3. finding the
circumference
or the
area

4. of a
circle
is an easy
thing to do!

5. You just need to
know a few simple
terms!

6. First-- center Circle O
A point in the exact middle of a circle—equal distances from all sides—used to name the circle.

7. Second-- diameter d=ab
A line segment whose ends touch the edge of the circle and goes through the center. 1 diameter = 2 radii

8. Third-- radius (radii) r=ao, bo, od
A line segment that goes from the center of a circle to the edge.
2 radii = 1 diameter or ½ diameter = 1 radii

9. Fifth-- d pi a b o h
pi = 3.14 or 22/7 g
the ratio of the diameter to the circumference of a circle. It has a value of about 3.14 or 22/7.

10. Fifth-- d pi a b o h
pi = 3.14 or 22/7 g
the ratio of the diameter to the circumference of a circle. It has a value of about 3.14 or 22/7.

11. circumference = pi times diameter
Now for the work!
circumference
C = d
This means
circumference = pi times diameter
The answer is in units.

12. Now for the work! circumference C = d C = 3.14 x 20 cm C~ 62.8 cm
Remember—it is about equal because 3.14 is not the complete value of pi.

13. Multiply the radius by 2 to get the diameter!
circumference
C = d
What if they only give you the value of the radius???
Multiply the radius by 2 to get the diameter!
16 cm
C = 3.14 x (16 cm x 2)
C~ cm

14. Area A = r 2 Which means pi times radius times radius.
10 cm
Remember—it is about equal because 3.14 is not the complete value of pi.