1. What’s Your Angle?

2. Background Vocabulary
plane: an infinite, flat surface
angles: two rays with a common endpoint
congruent angles: two angles that have equal measures
transversals: lines that intersect two or more lines (It’s the one line that both angles are touching.)
parallel lines: lines in a plane that never meet. l l is the symbol for parallel lines.

3. Complementary Angles
Two angles whose
measure add up
to 90°.
35°
55°

4. Supplementary Angles
Two angles whose
measures add up
to 180°.
90°
90°

5. Vertical Angles Vertical angles are diagonally across from each other.
Vertical angles are congruent.

6. Vertical Angles Angle 1 and Angle 4 are congruent angles. 1. 2. 3. 4.5. 6. 7. 8.
Angle 1 and Angle 4 are congruent angles.

7. Relationships Matter
When a transversal crosses two PARALLEL lines, we can say a lot about their angle measures.

8. When lines are parallel:1. 2. 3. 4. 5. 6. 7. 8.
= indicates lines are parallel

9. Alternate Interior Angles
Alternate Interior Angles are on “alternate” (opposite) sides and on the “interior” (inside) of the parallel lines.

10. Alternate Interior Angles
Alternate interior angles are congruent. 1. 2. 3. 4. 5. 6. 7. 8.
Angle 3 and Angle 6 are congruent angles. This means they have the same measure.

11. Alternate Exterior Angles
Alternate exterior angles are on “alternate” (opposite) sides and on the “exterior” (outside) of the parallel lines.

12. Alternate Exterior Angles
Alternate exterior angles are congruent. 1. 2. 3. 4. 5. 6. 7. 8.
Angle 1 and Angle 8 are congruent angles. This means they have the same measure.

13. Corresponding Angles
Corresponding angles are in the same relative location.

14. Corresponding Angles Angle 1 and Angle 5 are congruent angles.
Corresponding angles are congruent. 1. 2. 3. 4. 5. 6. 7. 8.
Angle 1 and Angle 5 are congruent angles.

15. Consecutive Interior Angles
Consecutive interior angles are next to each other (on the same side of the transversal) between the lines.

16. Consecutive Interior Angles
Consecutive interior angles are SUPPLEMENTARY. 1. 2. 3. 4. 5. 6. 7. 8.
Angle 4 and Angle 6 are supplementary angles. Together their measures = 180°

17. Demonstrate Your Knowledge
Now that you’ve seen what is
congruent, you can take the
measurement of “1” angle and figure
out the others. Let’s try it!

18. WHY?? Angle 2 measures 110°. What do the other angles measure? 1. 2.3. 4. 5. 6. 7. 8.
WHY??

19. Answers
70°
110°
110°
70°
70°
110°
70°
110°