The distance around a circle is called the ___________________________________.
Theorem 11.8: Circumference of a Circle
If a circle has a circumference of C units
and a radius of r units, then C  2 r .
Practice: The radius, diameter, or circumference of a circle is given. Find the other measures to the
nearest tenth.
1.) r = 7, d =
?
3.) C = 116.5, d =
,C=
?
?
,r=
?
2.) d = 32, r =
?
4.) r = 12, d =
?
,C=
,C=
Application: The dimensions of a car tire are shown. To the nearest foot,
how far does the tire travel when it makes 15 revolutions?
?___
?___
An ____________________________ is a portion of the circumference of a circle.
You can use the measure of the arc (in degrees) to find its length (in linear units)
Arc Length Formula – it’s a proportion!
arc length of AB mAB

2 r
360
**Ask yourself:
What PORTION of the whole circumference is this arc?
Practice: Find the length of each arc. Round to the nearest tenth.
a.
b.
d. Use the given information to find the circumference of Circle Z.
c.
Theorem 11.9: Area of a Circle
The area of a circle is  times the square of the radius.
Practice: Find the indicated measure.
1.
Area
2. Diameter
r = 2.5 cm
A = 113.1 cm2
A __________________________________ is the region bounded by two radii of the
circle and their intercepted arc.
Sector Area Formula – it’s a proportion!
area of sector APB mAB

2
r
360
**Ask yourself:
What PORTION of the whole area is this sector?
Examples: Find the indicated measure.
a. Area of
D.
b. Area of the smaller sector (FDE).
c. Area of the larger sector (FGED).
d. Find the area of sector RQS
e. Find the area of the entire circle.