Transcript Slide 1

Do Now 2/24/10
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Take out HW from last night.
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Text p. 295, #6-9 all, & 12
Copy HW in your planner.
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Text p. 295, #10-15 all
Quiz sections 6.4 & 6.5 Monday
Review “Geometry NJASK7 Prep” assignment on
MySkillsTutor – Quiz Friday
Homework
Text p. 295, #6-9 all, & 12
6) 24 inches
 7) 15 mm
 8) 9 cm
 9) 12.5 yd
 12) a. 63 in.
b. 15.75 ft.
or 15 ft. 9 in.
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Objective
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SWBAT find unknown side lengths of
similar figures using indirect
measurements
Section 6.4 “Similar and Congruent
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.
Properties of similar figures:
1). Corresponding angles are congruent
2). Corresponding sides are proportional (equal ratios)
Section 6.5 “Similarity and
Measurement”
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 ~ XYZ, find a and z.
Y
AC
AB
BC


XY
XZ
YZ
X
A
24
25
20
C
z
a
40
Z
B
BC
AB

YZ
XZ
a
25

24 40
40a  600
a  15
AC
AB

XY
XZ
20 25

z
40
25z  800
z  32
Indirect Measurements
You measure the shadow of a telephone pole to be 30 ft.
The shadow of a 6ft-tree is 4 ft. How tall is the telephone
pole?
H
30

6
4
Height pole Shadow pole

height tree
shadow tree
4 H  180
H  45
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
Using Algebra and Similar Triangles
Given ABC ~ DEC, find BE.
A
D
20
B
15
x
E
36
C
BC  BE  EC
AB
BC

EC
DE
20

15
x  36
36
Cross multiply
20 36  15( x  36)
720  15 x  540
180  15 x
12  x
Using Algebra and Similar Figures
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Find the length of BF
given that ABCD ~ CEFG.
B
x
F
FC CG

BC CD
18 cm
8
18

8  x 27
4cm
C
8 cm
E
A
G
D
9 cm
NJASK7 Prep
Homework
Text p. 296, #10-15 all