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Splash Screen
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Lesson Menu
Five-Minute Check (over Chapter 10) Then/Now New
Vocabulary Key Concept Pairs of Angles Example
1 Find a Missing Angle Measure Key Concept
Names of Special Angles Example 2 Find
Measures of Angles Formed by Parallel
Lines Example 3 Use Algebra to Find Missing
Angle Measures
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5-Minute Check 1
A. 5 B. 6 C. 7 D. 8
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5-Minute Check 2
Which list of numbers is correctly ordered least
to greatest?
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5-Minute Check 3
If c is the measure of the hypotenuse and a 6
and b 9, find the measure of c. Round to the
nearest tenth.
A. 10.5 units B. 10.8 units C. 11.3 units D. 12
units
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5-Minute Check 4
Find the distance between A(3, 4), and B(5,
2).Round to the nearest tenth.
A. 8.2 units B. 8.1 units C. 8.0 units D. 7.9
units
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5-Minute Check 5
What is the value of x? Classify the triangle by
its angles and by its sides.
A. 102 obtuse scalene B. 92 acute scalene
C. 90 right scalene D. 82 acute scalene
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Then/Now
You have already found the missing angle measure
of a triangle. (Lesson 103)

• Examine relationships between pairs of angles.

• Examine relationships of angles formed by
  parallel lines and a transversal.

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Vocabulary

• perpendicular lines

• transversal

• vertical angles
• adjacent angles
• complementary angles
• supplementary angles
• parallel lines

• alternate interior angles
• alternate exterior angles
• corresponding angles

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Concept A
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Example 1 A
Find a Missing Angle Measure
A. Jun is cutting a tile. Classify the
relationship of ?a and ?b.
Answer The angles are complementary. The sum of
their measures is 90.
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Example 1 B
Find a Missing Angle Measure
B. If m?a 53, what is the measure of ?b?
m?b 53 90 Write the equation. m?b
53 53 90 53 Subtract 53 from each side.
m?b 37 Simplify.
Answer m?b 37
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Example 1 CYP A
A. Elisa is cutting a piece of fabric. What is
the relationship between ?a and ?b?
A. They are complementary. B. They are
supplementary. C. They are congruent. D. They are
obtuse.
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Example 1 CYP B
B. If m?a 40, what is m?b?
A. 140 B. 220 C. 50 D. 90
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Concept B
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Example 2 A
Find Measures of Angles Formed by Parallel Lines
A. Classify the relationship between ?9 and ?13.
Answer Since ?9 and ?13 are corresponding
angles, they are congruent.
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Example 2
Find Measures of Angles Formed by Parallel Lines
B. If m?13 is 75, find m?11 and m?15.
Since ?13 and ?11 are alternate interior
angles, they are congruent. So, m?11 75. ?11
and ?15 are corresponding angles and are
congruent. So, m?15 75.
Answer m?11 75 and m?15 75
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Example 2 CYP A
A. What is the relationship between ?1 and ?5?
A. They are corresponding and congruent. B. They
are adjacent and supplementary. C. They are
corresponding and supplementary. D. They are
adjacent and congruent.
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Example 2 CYP B
B. If m?3 78, what is m?7?
A. 12 B. 22 C. 78 D. 102
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Example 3
Use Algebra to Find Missing Angle Measures
ALGEBRA Angles DEF and WXY are complementary
angles, with m?DEF 2x and m?WXY 3x 20.
Find the measures of ?DEF and ?WXY.
Step 1 Find the value of x.
m?DEF m?WXY 90 Complementary angles 2x
3x 20 90 Replace m?DEF with 2x and m?WXY
with 3x 20.
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Example 3
Use Algebra to Find Missing Angle Measures
Combine like terms.
Add 20 to each side.
Simplify.
Divide each side by 5.
Simplify.
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Example 3
Use Algebra to Find Missing Angle Measures
Step 2 Replace x with 22 to find the measure of
each angle.
m?DEF 2x m?WXY 3x 20 2(22)
or 44 3(22) 20 or 46
Answer m?DEF 44 and m?WXY 46
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Example 3
Angles RST and ABC are complementary angles with
m?RST 3x and m?ABC x 10. What are the
measures of ?ABC and ?RST?
A. m?ABC 12 and m?RST 78 B. m?ABC 20 and
m?RST 70 C. m?ABC 30 and m?RST
60 D. m?ABC 30 and m?RST 70
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End of the Lesson