Lesson 14.1: Angles Formed by Intersecting Lines

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.

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.

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

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.

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

Prove the Vertical Angle Theorem