Download 8.4--similar triangles notes

Geometry
Mrs. Blanco
Objectives
 Identify
 Use
similar triangles
similar triangles in reallife problems
Ex. 1: Writing Proportionality Statements
In the diagram,
∆BTW ~ ∆ETC
a) Write the statement
of proportionality.
ET TC EC
BT TW BW
b) Find m TEC.
T
E
C
3
20
m TEC = 79°
79
B
c) Find ET and BE
NEXT SLIDE
34
12
W
Ex. 1: Writing Proportionality Statements
In the diagram,
∆BTW ~ ∆ETC.
Find ET and BE.

c.
Write proportion.
3
ET
=
12
20
Substitute values.
5
= ET
34
E
CE
ET
=
WB
BT
3(20) = 12ET
T
3
20
Cross Multiply
Divide
C
79
B
So, ET is 5 units and BE is 15 units.
12
W
Postulate 25 Angle-Angle Similarity
Postulate

If two angles of one
triangle are congruent
to the two angles of
another triangle, then
the two triangles are
similar.
K
L
Y
J

If K
Y and J
X, then ∆JKL ~ ∆XYZ.
X
Z
Ex. 2: Are the two triangles similar? If so,
find x and y
Yes, ΔPQR~ΔLMN
x=24 and y=16
Ex. 3: Are the two triangles similar? If
so, write the similarity statement.
Ex. 4: Are the two triangles similar? If
so, write the similarity statement.
Ex. 5: Using Similar Triangles
BX= 0.75 miles
CX= 2.25 miles
Practice—
page 484 #18-26 even
page 485 #34-44 even
Take 15 minutes