Download Section 9.3 Similar Triangles

Geometry – Chapter 9 Lesson Plans
Section 9.3 – Similar Triangles
Enduring Understandings: The student shall be able to:
1. use AA, SSS, and SAS similarity tests for triangles.
Standards:
22. Similarity
Identifies similar figures in practical applications; identifies similar triangles and
other similar polygons by using their properties.
Essential Questions: What is required to prove two triangles are similar?
Warm up/Opener:
Activities:
We have three ways to prove triangles are similar.
1. Do the exercise of making two triangles with two congruent angles and different
lengths of included sides. Measure the lengths of the sides, and compare the
ratios of them. Are they similar? Yes, because the angles are congruent and the
ratios of the corresponding sides are the same.
AA: If two angles of one triangle are congruent to two angle of another triangle,
then the triangles are similar.
Do example 1 and 3 in the red book, pg 355 & 356.
2. SSS: If the measures of the corresponding sides of two triangles are proportional,
then the triangles are similar. Do an example or two.
3. SAS: If the measures of two sides of a triangle are proportional to the measures of
two corresponding sides of another triangle and the included angles are congruent,
then the triangles are similar. Do example 2 in the red book, pg 356.
Similarity of triangles is reflexive, symmetric, and transitive.
Assessments:
Do the “Check for Understanding” # 3, 4 and 5.
CW WS 7.3 of the red book and 9.3 of the Blue book
HW pg 366-367, # 6 - 17 all of the blue book and pg. 359, # 22 - 26 all of the red book.
(17) A version of one of the problems from the red book will be on the test as a bonus for
10 points. You will have to show your work to get credit.