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Lesson Plan #18
Date: Thursday October 10th, 2012
Class: Geometry
Topic: Proving triangles congruent by the S.A.S postulate
Aim: How do we prove triangles congruent by the S.A.S postulate?
HW #18:
Read pages 117-118, page 120 #’s 1, 4, 7, 10
Page 123 #’s 1-3
Objectives:
1) Students will be able to define congruent polygons.
2) Students will be able to define corresponding parts of congruent polygons
3) Students will be able to understand the S.A.S. postulate.
4) Students will be able to use the S.A.S. postulate to prove triangles congruent.
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Do Now: At right are two polygons (what type? _____________) where one
can be moved in such a way that the sides and angles of one polygon fit
exactly upon the sides and angles of the second polygon. How do we classify
these two polygons?
F
A
E
B
J
G
C
D
H
I
PROCEDURE:
Write the Aim and Do Now
Get students working!
Take attendance
Give Back HW
Collect HW
Go over the Do Now
In the congruent polygons, what vertex in the 2nd polygon corresponds to vertex A in the first polygon?
Name the other corresponding vertices
Name the corresponding sides
Definition: Two polygons are congruent if their vertices can be matched up so that the corresponding sides and angles (or
corresponding parts for short) of the polygons are congruent.
Let’s mark the corresponding parts in the congruent triangles below.
Indicate the corresponding parts of the congruent
triangles at right
Examine the two triangles at left with the indicated sides and angles
congruent. What do you notice about the two triangles?
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Postulate: Two triangles are congruent if two sides and the included angle of one triangle are congruent to two sides and
the included angle of the other [s.a.s.]≅[s.a.s.]
http://www.mathwarehouse.com/geometry/congruent_triangles/side-angle-side-postulate.php