1. Lesson 14.1: Angles Formed by Intersecting Lines

2. Geometry Vocab Review
Complementary Angles are two angles whose measures add up to 90 degrees. Supplementary Angles are two angles whose measures add up to 180 degrees. Congruent Angles are angles that have equal measure.

3. Linear Pairs of Angles
When two lines intersect, they form four angles. The angles that together form a straight line are called linear pairs of angles. Angle 1 and 2, Angle 2 and 3, Angle 3 and 4, and Angle 4 and 1 are linear pairs of angles.

4. Linear Pair Theorem
Linear pairs of angles are supplementary. Since angles 1 and 2 are a linear pair, then they are supplementary by the Linear Pair Theorem. The same can be said about any other linear pair

5. Vertical Angles
When two lines intersect to form four angles, the angles that are opposite each other are called vertical angles. Angles 1 and 3 are vertical angles. Angles 2 and 4 are vertical angles.

6. Vertical Angle Theorem
If two angles are vertical angles, then they are congruent. by vertical angle theorem

7. Prove the Vertical Angle Theorem