3.4 Parallel Lines and the Triangle Angle Sum Theorem 2011
October 17, 2011
3.4 Parallel Lines and the Triangle Angle­Sum Theorem
Objectives:
*Classify triangles and find the measures of their angles.
*Use exterior angles of triangles.
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3.4 Parallel Lines and the Triangle Angle Sum Theorem 2011
October 17, 2011
WARM­UP:
Classify each angle as acute, right, or obtuse.
3.
2.
1.
Solve each equation.
4. 30 + 90 + x = 180
5. 55 + x + 105 = 180
6. x + 58 = 90
7. 32 + x = 90
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3.4 Parallel Lines and the Triangle Angle Sum Theorem 2011
October 17, 2011
Activity:
• Draw and cut out a large triangle.
• Number the angles and tear them off.
• Place the three angles adjacent to each other to form one angle, as shown at the right.
1. What kind of angle is formed by the three smaller angles? What is its measure?
2. Make a conjecture about the sum of the measures of the angles of a triangle.
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3.4 Parallel Lines and the Triangle Angle Sum Theorem 2011
October 17, 2011
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3.4 Parallel Lines and the Triangle Angle Sum Theorem 2011
October 17, 2011
Example #1: Find the values of x, y, and z.
G
39o
F
65o
21o
xo yo zo
J
H
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3.4 Parallel Lines and the Triangle Angle Sum Theorem 2011
October 17, 2011
Classify each triangle by its angles.
Classify each triangle by its sides.
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3.4 Parallel Lines and the Triangle Angle Sum Theorem 2011
October 17, 2011
Example #2: Classify the triangle by its sides and its angles.
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3.4 Parallel Lines and the Triangle Angle Sum Theorem 2011
October 17, 2011
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3.4 Parallel Lines and the Triangle Angle Sum Theorem 2011
October 17, 2011
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3.4 Parallel Lines and the Triangle Angle Sum Theorem 2011
October 17, 2011
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3.4 Parallel Lines and the Triangle Angle Sum Theorem 2011
October 17, 2011
Example #3: Find each missing angle measure.
a.
b.
o
40
1
30o
113o
70o
2
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3.4 Parallel Lines and the Triangle Angle Sum Theorem 2011
October 17, 2011
Example #4:
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3.4 Parallel Lines and the Triangle Angle Sum Theorem 2011
October 17, 2011
Homework: page 150 (1 ­ 9, 18 ­ 27)
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