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Chapter 3 Lesson 1
Objective: To indentify angles formed
by two lines and a transversal.
transversal: a line that intersects two coplanar lines at two
distinct points.
t
l
m
transversal
alternate interior angles: nonadjacent interior angles that lie
on opposite sides of the transversal.
t
l
41
2 3
m
same-side interior angles: lie on the same side of the
transversal and between l and m.
t
l
41
2 3
m
corresponding angles: lie on the same side of the transversal
and in corresponding positions relative to l and m.
t
l
6
5
41
m
3
2
7 8
Example 1:
Identifying Angles
Name a pair of alternate interior angles and a pair of
same-side interior angles.
t
6
5
3 and 4 are alternate interior
4 1
angles
1 and 3 are same-side interior
angles.
2 3
7 8
l
m
Example 2:
Identifying Angles
Name all pairs of corresponding angles.
5 and 2; 4 and  7
;6 and 3; 1 and  8
t
56
4 1
2 3
7 8
l
m
Example 3:
Identifying Angles
Identify which angle forms a pair of same-side interior angles
with  1. Identify which angle forms a pair of corresponding
angles with  1.
Same-Side
41
3 2
8 5
7 6
8
Corresponding
5
Postulate 3-1: Corresponding Angles Postulate
If a transversal intersects two parallel lines, then
corresponding angles are congruent.
t
1
► l
1  2
2
► m
Theorem 3-1: Alternate Interior Angles Theorem
If a transversal intersects two parallel lines, then alternate
interior angles are congruent.
t
1
2
►
l
►
m
1  2
Theorem 3-2: Same-Side Interior Angles Theorem
If a transversal intersects two parallel lines, then same-side
interior angles are supplementary.
t
► l
1
2
►
m
m1  m2  180
Homework
pg.118-120
#1-8; 9-22;26;28