Download Geometry Fall 2011 Lesson 17 (S.A.S. Postulate)

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Lesson Plan #38
Date: Wednesday December 9th, 2015
Class: Geometry
Topic: Exterior angle of a triangle
Aim: What is the relationship between an exterior angle of a triangle and its 2 remote interior angles of the triangle?
Objectives:
1)
Students will be able to use the relationship between an exterior angle of a triangle and the 2 remote interior angles of the triangle to
solve problems.
HW#38:
Do Now:
Statements
1.
Reasons
1.
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PROCEDURE:
Write the Aim and Do Now
Get students working!
Take attendance
Give Back HW
Collect HW
Go over the Do Now
Assignment #1: Complete the proof below
Given: ∆𝐴𝐵𝐶 with exterior < 𝐶𝐵𝐷 at vertex 𝐵
Two non-adjacent interior angles < 𝐴 and < 𝐶
Prove: 𝑚 < 𝐶𝐵𝐷 = 𝑚 < 𝐴 + 𝑚 < 𝐶
Statements
1. ∆𝐴𝐵𝐶 with exterior < 𝐶𝐵𝐷 at vertex 𝐵
1.
Reasons
2. < 𝐶𝐵𝐷 and < 𝐶𝐵𝐴 form a linear pair
2. A linear pair of angles are two angles whose sum is a straight angle (1)
3. < CBD and < CBA are supplementary
3. If two angles form a linear pair, then they are supplementary (2)
4. 𝒎 < 𝐶𝐵𝐷 + 𝑚 < 𝐶𝐵𝐴 = 180
4.
5. 𝒎 < 𝐴 + 𝑚 < 𝐶𝐵𝐴 + 𝑚 < 𝐶 = 180
5.
6.𝒎 < 𝐶𝐵𝐷 + 𝑚 < 𝐶𝐵𝐴 = 𝒎 < 𝐴 + 𝑚 < 𝐶𝐵𝐴 + 𝑚 < 𝐶
6.
7.𝑚 < 𝐶𝐵𝐷 = 𝑚 < 𝐴 + 𝑚 < 𝐶
7.
Link: http://hotmath.com/hotmath_help/topics/exterior-angle-theorem.html
Theorem:
The measure of an exterior angle of a triangle is equal to the sum of the measures of the two nonadjacent interior angles.
Online Interactive Activity : Let’s go http://www.mathopenref.com/triangleextangletheorem.html
and see the relationship between an exterior angle of a triangle and the two remote interior angles.
Together #1:
Together #2:
Find the measure of the angle labeled c.
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On Your Own 1:
If the measure of the exterior angle = 3x  10 degrees and the measure of the two remote interiors
angles are 25 degrees and  x  15 degrees, find x .
On Your Own 2:
On Your Own 3:
Past Regents Question:
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Group Work:
27)
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If enough time:
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