Introduction: When two lines intersect they form four angles with a common vertex. Look at the scissors below. Can you see how the handles and blades cross and create four angles similar to the intersecting lines shown?

When taken in pairs, these angles have special relationships. For example, `ang1` and `ang2` are adjacent supplementary angles. Together, this angle pair forms a straight angle. There are three other pairs of adjacent supplementary angles in the diagram. Can you find them?

Vertical angles are a pair of non-adjacent angles formed by intersecting lines. `ang1` and `ang3` are vertical angles. `ang2` and `ang4` are also vertical angles. 

Look at one set of vertical angles above. How do the sizes of the two angles compare? If you said they look the same, you are correct! Vertical angles are congruent. If you measure `ang1` and `ang3` with a protractor, you should find that each measures `110deg`.

By using the fact that vertical angles are congruent and combining it with facts about supplementary angles, we can solve for unknown angles in a figure.

Directions for This Lesson: In this lesson, you will learn about vertical angles. First, try the practice questions to determine what you already know. Then, watch the video lesson to learn more. Finally, try what you learned in the activity and practice sections. 

 

Practice what you have learned by completing the post-lesson worksheet.