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Comp book
3.1 Parallel Lines and Transversals
Essential Question: How do we use parallel lines and transversals to
identify angle measures?
Take out 4 different colored pencils from blue
box…or your own
Complementary Angles = When sum of two angles equals 90°
O
R
N
E
R
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Comp book
Supplementary Angles = Straight When sum of two angles equals 180°
Vocabulary
Comp book
Parallel Lines – Lines in the same plane that do not intersect
P || Q
The symbol || means
“is parallel to.”
Perpendicular Lines – Intersecting lines whose angle measures 90°
L⊥M
The symbol ⊥ means
“is perpendicular to.”
Transversal: a line that intersects two or more lines. Comp book
Transversals to parallel lines form special angle pairs.
A ll B
A
B
Adjacent angles: (next door & supplementary = 180)
1 & 2
2 & 3
3 & 4
4 & 1
1
4
5
5 & 6
5 & 8
6 & 7
7 & 8
8
6
7
2
3
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Vertical angles: (opposite & congruent)
1  3
2  4
1
4
5  7
6  8
5
8
6
7
2
3
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Corresponding angles:
d
a
c
b
f
e
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If parallel lines are crossed by a transversal then
Common
Mistake
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corresponding
angles
are congruent
Corresponding:
Not Corresponding:
*because lines are parallel*
because lines are not parallel*
2
1
3
1
4
5 6
7 8
2
3 4
5 6
7 8
Interior angles:
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Exterior angles:
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Subtract known angle (100
degrees) from 180 degrees to
find its supplementary
adjacent angle
80
80 and 100 form
supplementary angle
100 80
Vertical angles are congruent
100 80
80
100 80
80 100
100 80
80
Corresponding angles
from one of the
parallel lines are all
congruent to their
corresponding angles
on the second parallel
line
FindQuick
missingQuiz
variable
Let’s Review
Find the value of x.
(x + 12)0
660
FindQuick
missingQuiz
variable
Let’s Review
120
(x + 50)