Transcript 7.3 Proving Triangles Similar

7.3 Proving Triangles Similar
• Objectives
• By the end of this lesson, I will be able to use
the AA~ postulate, as well as the SAS~ and
SSS~ Theorems when dealing with similar
triangles
• I will also be able to use similarity to
ingeniously find indirect measurements
7.3 Proving Triangles Similar
• Angle-Angle Similarity (AA ~) Postulate
– If two angles of one triangle are congruent to two
angles of another triangle, then the triangles are
similar.
Using the AA ~ Postulate
• Are the two triangles similar? How do you know?
a. Triangle RSW and Triangle VSB.
b. Triangle JKL and Triangle PQR.
a. Similar
b. Not similar.
Side-Angle-Side Similarity (SAS ~)
Theorem
• If an angle of one triangle is congruent to an angle of
a second triangle, and the sides that include the two
angles are proportional, then the triangles are
similar.
Side-Side-Side Similarity (SSS ~ )
Theorem
• If the corresponding sides of two triangles are
proportional, then the triangles are similar.
Verifying Triangle Similarity
• Are the triangles similar? If so, write a similarity
statement for the triangles.
• Yes, Triangle STU ~ Triangle XVW by the SSS Similarity
Theorem.
Verifying Triangle Similarity
• Are the triangles similar? If so, write a similarity
statement for the triangles.
• Yes, Triangle KLP ~ Triangle KMN by the SAS Similarity
Theorem.
Indirect Measurement
• You can use indirect measurement to find
lengths that are difficult to measure directly.
– One method of indirect measurement uses the
fact that light reflects off a mirror at the same
angle at which it hits the mirror.
Finding the Length of Similar Triangles
• Before rock climbing, Darius wants to know how high he will climb.
He places a mirror on the ground and walks backward until he can
see the top of the cliff in the mirror. What is the height of the cliff?
Finding Lengths in Similar Triangles
Triangle HTV ~ Triangle JSV – AA~ Postulate
HT TV

JS SV
5.5 6

x 34
187  6x
x  31.2
More Practice!!!!!
• In-class practice: Textbook p. 455 – 456 # 7 –
12, 15, 16, 17.
• Additional Assignment : MathXL assignment
(which includes tomorrow’s 7.4 lesson) due
Wednesday 1/13/2016
• Exit ticket…….