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.
Concept
Use Corresponding Angles Postulate Example 1 A. In the figure, m11 = 51. Find m15. Tell which postulates (or theorems) you used. What is the relationship between < 11 and < 15? 15 11 Corresponding Angles Postulate m15 = m11 Definition of congruent angles m15 = 51 Substitution m< 15 = 51
Use Corresponding Angles Postulate Example 1 B. In the figure, m11 = 51. Find m16. Tell which postulates (or theorems) you used. 16 15 Vertical Angles Theorem 15 11 Corresponding Angles Postulate 16 11 Transitive Property () m16 = m11 Definition of congruent angles m16 = 51 Substitution
Example 1b B. In the figure, a || b and m18 = 42. Find m25. A. 42 C. 48 D. 138
Concept
Example 2 Use Theorems about Parallel Lines FLOOR TILES The diagram represents the floor tiles in Michelle’s house. If m2 = 125, find m3. 2 3 Alternate Interior Angles Theorem m2 = m3 Definition of congruent angles 125 = m3 Substitution Answer: m3 = 125
Example 2 FLOOR TILES The diagram represents the floor tiles in Michelle’s house. If m2 = 125, find m4. A. 25 B. 55 C. 70 D. 125
Skills Packet Do #4 - #6
Example 3 A. ALGEBRA If m5 = 2x – 10, and m7 = x + 15, find x. Find Values of Variables Example 3 A. ALGEBRA If m5 = 2x – 10, and m7 = x + 15, find x. 5 7 Corresponding Angles Postulate m5 = m7 Definition of congruent angles 2x – 10 = x + 15 Substitution x – 10 = 15 Subtract x from each side. x = 25 Add 10 to each side. Answer: x = 25
Example 3 B. ALGEBRA If m4 = 4(y – 25), and m8 = 4y, find y. Find Values of Variables Example 3 B. ALGEBRA If m4 = 4(y – 25), and m8 = 4y, find y. 8 6 Corresponding Angles Postulate m8 = m6 Definition of congruent angles 4y = m6 Substitution
Example 3 m6 + m4 = 180 Supplement Theorem Find Values of Variables Example 3 m6 + m4 = 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
Example 3 A. ALGEBRA If m1 = 9x + 6, m2 = 2(5x – 3), and m3 = 5y + 14, find x.
Skills Packet Do #7 - #11