Geo 10.1 Circles and Circumference
Name _________________________
Learning Objective: After this lesson, you should be able to successfully identify and use parts of circles.
You should also be able to find the circumference of a circle.
Standard: G.CO.1 Know precise definitions of angle, circle, perpendicular line, parallel line, and line segment, based on
the undefined notions of point, line, distance along a line, and distance around a circular arc.
G.C.2 Identify and describe relationships among inscribed angles, radii, and chords.
For Exercises 1- 7, refer to P.
1. Name the circle.
2. Name a radius.
3. Name a chord.
4. Name a diameter.
5. Name a radius not drawn as part of a diameter.
6. Suppose the diameter of the circle is 16 cm. Find the radius.
7. If PC = 11 in, find AB.
The diameters of F and G are 5 and 6 units, respectively. Find each measure.
8. BF
9. AB
Find the diameter and radius of a circle with the given circumference. Round to the nearest hundredth.
10. C = 36 m
11. C = 17.2 ft
12. C = 5 yd
Find the exact circumference of each circle using the given inscribed or circumscribed polygon.
13.
14.
15.
16.
17.
18.
19. SUNDIALS Herman purchased a sundial to use as the centerpiece for a garden. The diameter of the
sundial is 9.5 inches.
a) Find the radius of the sundial.
b) Find the circumference of the sundial to the nearest hundredth.
20. COINS Three identical circular coins are lined up in a row as shown. The distance between the centers of
the first and third coins is 3.2 centimeters. What is the radius of one of these coins?
21. PLAZAS A rectangular plaza has a surrounding circular fence. The diagonals of the rectangle pass from
one point on the fence through the center of the circle to another point on the fence. Based on the
information in the figure, what is the diameter of the fence? Round your answer to the nearest tenth of a
foot.
22. EXERCISE HOOPS Taiga wants to make a circular loop that he can twirl around his body for exercise. He
will use a tube that is 2.5 meters long.
a) What will be the diameter of Taiga's exercise hoop? Round your answer
to the nearest thousandth of a meter.
b) What will be the radius of Taiga's exercise hoop? Round your answer to
the nearest thousandth of a meter.
Answers: 1. P
15. 10 2 
3. AB, DE
17. 58  mi
5. PC
19a) 4.75 in
7. 22 in
9. 2
b) 29.83 in
11. d = 5.48 ft, r = 2.74 ft
21. 449.6 ft
13. 3 2  cm