This document contains notes from a math lesson on calculating the areas of circles, sectors, segments, and annuli. It defines these shapes and provides their area formulas. Examples are worked through, such as finding the radius of a circle given its area and the area of a shaded sector region.

1. 11.5 Area of Sectors
HW pg. 758 #3­31 odds
April 02, 2015
Bellwork
about 56.5 cm.
8.64 cm
100.53 cm
7.64 ft

2. 11.5 Area of Sectors
HW pg. 758 #3­31 odds
April 02, 2015
A circle has an area of ≈ 38.485 in2
.
What is the circumference of the circle?
11.5 Areas of Circles & Sectors
Area of Circle = πr2
(fuzzy wuzzy)
4.2 m

3. 11.5 Area of Sectors
HW pg. 758 #3­31 odds
April 02, 2015
20 in
Find the area of the shaded region.
10 cm

4. 11.5 Area of Sectors
HW pg. 758 #3­31 odds
April 02, 2015
Sector of a Circle:
region bounded by 2 radii of a circle & the included arc
Formula for the Area of a Sector:
“portion of the circle times the area of the circle”
Asector =
x
360
πr2
r = 3 cm
120
o
r = 6cm
60
o

5. 11.5 Area of Sectors
HW pg. 758 #3­31 odds
April 02, 2015
Segment of a Circle:
region bounded by a chord of a circle
& the included arc
r = 8 cm

6. 11.5 Area of Sectors
HW pg. 758 #3­31 odds
April 02, 2015
Annulus:
region bounded by two concentric circles

7. 11.5 Area of Sectors
HW pg. 758 #3­31 odds
April 02, 2015
R = 12cm
r = 9 cm
r
60o
R
The shaded area is 12π cm2.
Find r.
r
120o

8. 11.5 Area of Sectors
HW pg. 758 #3­31 odds
April 02, 2015
11.5 HW pg. 758 #3-31 odds