1. Warm Up
Problem of the Day
Lesson Presentation
Lesson Quizzes

2. Warm Up Complete each sentence.
1. Angles whose measures have a sum of 90° are _______________ .
2. Vertical angles have equal measures, so they are ______________.
3. Angles whose measures have a sum of 180° are ______________.
4. An angle that measures less than 90° is a(n) ____________ angle.
complementary
congruent
supplementary
acute

3. Problem of the Day
The square root of 1,813,141,561 is a whole number. Is it odd or even? How do you know?
Odd: An odd number can only be the product of two odd numbers.

4. Learn to identify parallel and perpendicular lines and the angles formed by a transversal.

5. Vocabulary
parallel lines
perpendicular lines
transversal

6. Parallel lines are lines in a plane that never meet, like a set of perfectly straight, infinite train tracks.
Perpendicular lines are lines that intersect at 90° angles.

7. The sides of the windows are transversals to the top and bottom.
The top and bottom of the windows are parallel.
A transversal is a line that intersects two or more lines that lie in the same plane. Transversals to parallel lines form angles with special properties.

8. You cannot tell if angles are congruent by measuring because measurement is not exact.
Caution!

9. Additional Example 1: Identifying Congruent Angles Formed by a Transversal
Measure the angles formed by the transversal and parallel lines. Which angles seem to be congruent?
1, 3, 5, and 7 all measure 150° and appear to be congruent.
 2, 4, 6, and 8 all measure 30° and appear to be congruent.

10. Additional Example 1 Continued
Angles circled in blue appear to be congruent to each other, and angles circled in red appear to be congruent to each other. 7 8

11. Check It Out: Example 1
Measure the angles formed by the transversal and parallel lines. Which angles seem to be congruent? 1 2 3 4 5 6 7 8
1, 4, 5, and 8 all measure 36° and appear to be congruent.
 2, 3, 6, and 7 all measure 144° and appear to be congruent.

12. Check It Out: Example 1 Continued
Angles marked in blue appear to be congruent to each other, and angles marked in red appear to be congruent to each other. 8 7 1 2 3 4 5 6 7 8

13. Some pairs of the eight angles formed by two parallel lines and a transversal have special names.

15. The symbol for parallel is ||. The symbol for perpendicular is .
Writing Math

16. Additional Example 2A: Finding Angle Measures of Parallel Lines Cut by Transversals
In the figure, line l || line m. Find the measure of the angle. 4
The 124 angle and 4 are corresponding angles.
m4 = 124°

17. Additional Example 2B: Finding Angle Measures of Parallel Lines Cut by Transversals Continued
In the figure, line l || line m. Find the measure of the angle. 2
2 is supplementary to angle 124°.
m ° = 180°
–124° –124°
m = 56°

18. Additional Example 2C: Finding Angle Measures of Parallel Lines Cut by Transversals Continued
In the figure, line l || line m. Find the measure of the angle. 6
6 is supplementary to angle 6.
m ° = 180°
–124° –124°
m = 56°
m6 = 56°

19. m7 = 144° Check It Out: Example 2A
In the figure, line n || line m. Find the measure of the angle. 7
The 144 angle and 7 are alternate exterior angles. 1
144° 3 4 5 6 7 8 m n
m7 = 144°

20. Check It Out: Example 2B
In the figure, line n || line m. Find the measure of the angle. 1
1 is supplementary to the 144° angle. 1
144° 3 4 5 6 7 8 m n
m ° = 180°
–144° –144°
m = 36°

21. m5 = 36° Check It Out: Example 2C
In the figure, line n || line m. Find the measure of the angle. 5
5 and 1 are corresponding angles. 1
144° 3 4 5 6 7 8 m n
m5 = 36°

22. Lesson Quiz for Student Response Systems
Lesson Quizzes
Standard Lesson Quiz
Lesson Quiz for Student Response Systems 22

23. Lesson Quiz
In the figure, a || b.
1. Name the angles congruent to 3.
1, 5, 7
2. Name all the angles supplementary to 6.
1, 3, 5, 7
3. If m1 = 105° what is m3?
105°
4. What is m6?
75°

24. Lesson Quiz for Student Response Systems
1. In the figure, x || y. Identify the angles congruent to 3.
A. 1, 2, 4
B. 2, 4, 6
C. 4, 5, 6
D. 1, 5, 8 24

25. Lesson Quiz for Student Response Systems
2. In the figure, x || y. If m5 = 115°, what is m7?
A. 25°
B. 65°
C. 75°
D. 115° 25