1. 3.3 Parallel Lines & Transversals
3.3 Parallel Lines and Transversals
3.3 Parallel Lines & Transversals
Define transversal, alternate interior angles, alternate exterior angles, same-side interior angles, and corresponding angles.
Make conjectures and prove theorems by using postulates and properties of parallel lines and transversals.

2. Theorems, Postulates, & Definitions
3.3 Parallel Lines and Transversals
Theorems, Postulates, & Definitions
Corresponding Angles Postulate : If two lines cut by a transversal are parallel, then corresponding angles are congruent.
corresponding angles
2  3

3. Theorems, Postulates, & Definitions
3.3 Parallel Lines and Transversals
Theorems, Postulates, & Definitions
Alternate Interior Angles Theorem:
If two lines cut by a transversal are parallel, then
alternate interior angles are congruent.
alternate interior angles
1  3

4. Theorems, Postulates, & Definitions
3.3 Parallel Lines and Transversals
Theorems, Postulates, & Definitions
Alternate Exterior Angles Theorem:
If two lines cut by a transversal are parallel,
then alternate exterior angles are congruent.
alternate exterior angles
2  5

5. Theorems, Postulates, & Definitions
3.3 Parallel Lines and Transversals
Theorems, Postulates, & Definitions
Same-Side Interior Angles Theorem:
If two lines cut by a transversal are parallel, then
same-side interior angles are supplementary.
same-side interior angles
1 + 4 = 180
GSP Example

6. Key Skills Identify special pairs of angles. Corresponding angles
3.3 Parallel Lines and Transversals
Key Skills
Identify special pairs of angles.
Corresponding angles
1 and 5
1 and 3
Alternate interior angles
Same-side interior angles
1 and 4
Alternate exterior angles
2 and 5

7. Key Skills Find angle measures formed by parallel lines
3.3 Parallel Lines and Transversals
Key Skills
Find angle measures formed by parallel lines
and transversals.
m || n and m1 = 135°.
Then m2 = m3 = m5 = 135° and m4 = 45°.