# Arc Length and Sectors of circles

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```					  STAR REVIEW---DO NOW!
Complete problems:
______________________________
Homework Correction

You know the drill…pass your paper back
to the person sitting directly behind you.
Class Exercises
p. 277 # 7                          p. 291 # 13, 14

50cm2
7) A = ___________________                    72cm2
13) A = ___________________

24m2
14) A = ___________________
Class / Homework
p. 278 # 8 - 11

8)            120in2
A = ___________________

32cm2
9) A = ____________________

116cm2
10) A = ____________________

75in2
11) A = ___________________
Worksheet 9.6
Worksheet 9.6
Worksheet 9.7
Worksheet 9.7
Circle Review Vocabulary (from chapter 2 p. 39)

A chord passing through the center
Circles
diameter

center

radius
A segment joining the center to any point on the circle
TODAY…& next class
Circumference = distance AROUND a circle

Circles
Area = space INSIDE a circle
Important Formulas
C  d                   3.14       or  
22
7
Find the Circumference of this circle
d=6
C  6
6
C = 6(3.14)

C  18.84 units
Find the Circumference

C  d
C  12(3.14)

C = 37.68 inches
What if I don’t know the diameter?
Remember, radius =½ diameter or 2radii = diameter
find the circumference
C  2 r
C = 2(3.14)(8)
8 cm

C = 50.24 cm
What about that other value for Pi?
22
find the circumference               or  
7

C  d
2
 22 
14 in          C  14  
 7 

C = 44 in
Class Work – do NOW

page 283 # 1-7

REMEMBER- “SHOW ME THE WORK”
is my middle name

Clever, Mrs. D
Class / Homework

Worksheet 9.8

Change in problem # 7:
22
use  =
7
Remember, everyone –SHOW ME the WORK!!!
MORE Important Formulas

Area of a circle       A r       2

  3.14
A   3       2                   3

22
or  
A = 3.14(9)               7

A = 28.26 sq units
MORE practice

Area of a circle      A r   2

use   3.14
A   9       2

18”
A = 3.14(81)

A = 254.34 sq in                    r=? 9
Tricky problem
Find the area of the shaded region
A r      2

1                                         use   3.14
A     (6) 2

4
6m

A = (¼) (36)(3.14)
Shaded region = ¼ of the circle
A = 28.26 sq m
Another Tricky problem
Find the area of the shaded region
A r     2

2
1 7                                                22
A                                            use  
 3  2                        3½
7
7
 1  22  49 
A     
 3  7  4                                 1
Shaded region = of the circle
3
A = 12.83 sq units
Another Tricky problem
Find the area of the shaded region
A r         2
 1  22 
A     14 
2

 8  7                                                    22
use  
45
45
14 in                      7
28
 1   22   196 
A                                             Shaded region =
 8  7  1 
45 1

360 8
A = 77 sq units
Another Tricky problem
Find the area of the shaded region
A r      2

1
A     (12) 2
60           use   3.14
6                           12 cm

1
A    (3.14)(144)                             Shaded region =
6                                             60 1

A = 75.36 sq units                                360 6
What if you can’t use a calculator?

A=    r2         That means….radius x radius x 3.14

I said….radius times radius times three(3) point one(1) four(4)

Again?….radius times radius times three(3) point one(1) four(4)
Class Work – do NOW

page 287 find exact area only # 1-5

Remember, show me work!!!
tonight’s homework

Worksheet 9.9 # 1-13

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