Transcript Slide 1
Do Now 4/4/11
Copy HW in your planner.
• Text p. 295, #6-12 all
Be ready to copy POTW #2.
Get your calculator from the back of the room.
Objective SWBAT find unknown side lengths of similar figures using proportions
Section 6.5 “Similarity and Measurement”
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)
Given ABCD ~ GHIJ, find HJ.
AB GH
BD HJ
12 30 16
x
12
x
480
x
40 Cross multiply G 30 I J A C 12 D B 16 x H
b C A Given ABC ~ DEF, find a.
Given ABC ~ DEF, find b.
D 20 32 F a B 40 35
a
35 32 40
b
20 32 40 40
a
1120
a
28 40
b
640
b
16
E
A 20 C Given ABC ~ XYZ, find g and f.
Z f 24 40 Y 25 g B X
BC YZ
AB XZ g
24 25 40 40
g g
15 600
AC
XY AB XZ
20
f
25 40 25
f f
32 800
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?
Height height pole
Shadow tree pole shadow tree H
5 24 4
H
4
H H
120 30
S h 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 h building flagpole
S s building flagpole H
50 55 10
H
10
H H
2750 275
h S s
A 20
Using Algebra and Similar Triangles
Given ABC ~ DEC, find BE.
D
BC
BE
EC
15 B
x
E
AB
DE BE
EC EC
20 15
x
36 36 Cross multiply
36
20 36 15 (
x
36 ) 720 15
x
540 180 15
x
12
x
C
NJASK7 Prep Homework
Text p. 296, #6-9 all