3.4 Parallel Lines and the Triangle Angle Sum Theorem 2010 October 05, 2010
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 2010 October 05, 2010
Check Skills You'll Need
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 2010 October 05, 2010
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 2010 October 05, 2010
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3.4 Parallel Lines and the Triangle Angle Sum Theorem 2010 October 05, 2010
Example #1: Find the values of x, y, and z.
G
39o
F
65o
21o
x o y o zo
J
H
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3.4 Parallel Lines and the Triangle Angle Sum Theorem 2010 October 05, 2010
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 2010 October 05, 2010
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 2010 October 05, 2010
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3.4 Parallel Lines and the Triangle Angle Sum Theorem 2010 October 05, 2010
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3.4 Parallel Lines and the Triangle Angle Sum Theorem 2010 October 05, 2010
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 2010 October 05, 2010
Example #4:
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3.4 Parallel Lines and the Triangle Angle Sum Theorem 2010 October 05, 2010
Homework: page 150 (1 ­ 9, 18 ­ 27)
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3.4 Parallel Lines and the Triangle Angle Sum Theorem 2010 October 05, 2010
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