1. Then/Now
You named angle pairs formed by parallel lines and transversals.
Use theorems to determine the relationships between specific pairs of angles.
Use algebra to find angle measurements.

2. Concept

3. Use Corresponding Angles Postulate
Example 1
A. In the figure, m11 = 51. Find m15. Tell which postulates (or theorems) you used.
What is the relationship between < 11 and < 15?
15  11 Corresponding Angles Postulate
m15 = m11 Definition of congruent angles
m15 = 51 Substitution
m< 15 = 51

4. Use Corresponding Angles Postulate
Example 1
B. In the figure, m11 = 51. Find m16. Tell which postulates (or theorems) you used.
16  15 Vertical Angles Theorem
15  11 Corresponding Angles Postulate
16  11 Transitive Property ()
m16 = m11 Definition of congruent angles
m16 = 51 Substitution

5. Example 1b B. In the figure, a || b and m18 = 42. Find m25. A. 42
C. 48
D. 138

6. Concept

7. Example 2
Use Theorems about Parallel Lines
FLOOR TILES The diagram represents the floor tiles in Michelle’s house. If m2 = 125, find m3.
2  3 Alternate Interior Angles Theorem
m2 = m3 Definition of congruent angles
125 = m3 Substitution
Answer: m3 = 125

8. Example 2
FLOOR TILES The diagram represents the floor tiles in Michelle’s house. If m2 = 125, find m4.
A. 25
B. 55
C. 70
D. 125

9. Skills Packet Do #4 - #6

10. Example 3 A. ALGEBRA If m5 = 2x – 10, and m7 = x + 15, find x.
Find Values of Variables
Example 3
A. ALGEBRA If m5 = 2x – 10, and m7 = x + 15, find x.
5  7 Corresponding Angles Postulate
m5 = m7 Definition of congruent angles
2x – 10 = x Substitution
x – 10 = 15 Subtract x from each side.
x = 25 Add 10 to each side.
Answer: x = 25

11. Example 3 B. ALGEBRA If m4 = 4(y – 25), and m8 = 4y, find y.
Find Values of Variables
Example 3
B. ALGEBRA If m4 = 4(y – 25), and m8 = 4y, find y.
8  6 Corresponding Angles Postulate
m8 = m6 Definition of congruent angles
4y = m6 Substitution

12. Example 3 m6 + m4 = 180 Supplement Theorem
Find Values of Variables
Example 3
m6 + m4 = 180 Supplement Theorem
4y + 4(y – 25) = 180 Substitution
4y + 4y – 100 = 180 Distributive Property
8y = 280 Add 100 to each side.
y = 35 Divide each side by 8.
Answer: y = 35

13. Example 3
A. ALGEBRA If m1 = 9x + 6, m2 = 2(5x – 3), and m3 = 5y + 14, find x.

14. Skills Packet Do #7 - #11