Transcript Slide 1

Do Now 1/11/12
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Take out your HW from last night.
 Text p. 166, #1-19 all, 23 &24
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Copy HW in your planner.
 Text p. 170, #1-11 all, 14-16 all
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In your journal, tell whether the figures are similar.
119°
59°
59°
55°
35°
86°
86°
35°
107°
80°
107°
79°
135°
38°
Try it out
Tell whether the figures are similar.
119°
59°
59°
35°
107°
55°
86°
86°
35°
107°
80°
79°
135°
38°
NP ? NO ? PO
=
=
QS
QR RS
7 ? 4 ? 6
=
=
14
12
8
? 1 ? 1
1 =
=
2
2
2
Similar
Not similar;
corresponding
angles do not have
equal measures
Homework
Text p. 166, #1-19 all, 23 &24
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1) similar
2) not similar
3) similar
4) not similar
5) not similar
6) similar
7) similar
8) not similar
9) No, corresponding angles are
not equal
10) 4 in. X 6 in., 16 in. X 24 in.
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11) similar
12) not similar
13) yes
14) no
15) yes
16) yes
17) no
18) no
19) no
23) C
24) No
Objective
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SWBAT use similar figures to find
unknown measures
Section 4.4 “Similar Figures”
Similar Figures
Two figures are SIMILAR FIGURES if they have the
same shape but not necessarily the same size. The
symbol ~ indicates two figures are similar.
Two figures are similar if:
1). The measures of their corresponding angles are equal
2). The ratios of the lengths of their corresponding sides
are proportional (equal ratios)
Section 4.5 “Using Similar Figures”
Given ABC ~ JKL, find x and y.
AB
BC

KJ
KL
8
12

28
x
8 x  336
x  42
Angle B corresponds to Angle K
Cross
multiply
y = 103°
Given ABCD ~ GHIJ, find HJ.
AB BD

GH HJ
12
16

30
x
30
G
x
I
J
Cross multiply
12
A
12x  480
x  40
H
B
16
C
D
Given ABC ~ DEF, find a.
Given ABC ~ DEF, find b.
D
A
20
32
b
C
40
F
B
a
E
35
a
32

35 40
40a  1120
a  28
b
32

20 40
40b  640
b  16
Given ABC ~ XYZ, find g and f.
Z
f
X
A
24
40
Y
25
20
C
g
BC
AB

YZ
XZ
g
25

24 40
40g  600
AC
AB

XY
XZ
20 25

f
40
25 f  800
f  32
g  15
B
Indirect Measurement
the method of using proportions to find
an unknown length or distance in
similar figures
Indirect Measurements
You measure the shadow of a telephone pole to be 24 ft.
The shadow of a 5ft-tree is 4 ft. How tall is the telephone
pole?
H
24

5
4
Height pole Shadow pole

height tree
shadow tree
4 H  120
H  30
H
h
S
s
Indirect Measurements
To estimate the height of the Transco Tower in Houston, TX,
you measure its shadow to be about 55m. The shadow of a
50m flagpole is about 10m. Estimate the height of the
Transco Tower.
H
55

50 10
H building S building

h flagpole s flagpole
10H  2750
H  275
H
h
S
s
Indirect Measurements
City officials want to know the height of a traffic light.
Estimate the height of the traffic light.
27.25 = 48.75
h
15
Write a proportion.
27.25h = 731.25
Cross multiply.
h ft
27.25 ft
48.75 ft
h ≈ 27 ft
The traffic light is about 27 feet tall.
Divide each side by
27.25 to isolate the
variable.
NJASK7 Prep
Homework
Text
p. 170, #1-11 all, 14-16 all