Proving Lines Parallel Section 3-5

Warm Up State the converse of each statement. 1. If a = b, then a + c = b + c. 2. If mA + mB = 90°, then A and B are complementary. 3. If AB + BC = AC, then A, B, and C are collinear. If a + c = b + c, then a = b. If A and  B are complementary, then mA + mB =90°. If A, B, and C are collinear, then AB + BC = AC.

Write the converse of: “If 2 ║ lines are cut by a transversal, then corresponding angles are congruent.”

Example: Use the Corresponding Angles Postulate and the given information to show that ℓ || m. m1 = m3 1  3 ℓ || m

4  8 Example: Use the given information to show that ℓ || m.

Example: Use the given information to show that ℓ || m. m3 = (4x – 80)°, m7 = (3x – 50)°, x = 30 3  7 ℓ || m

Example: Determining Whether Lines are Parallel Use the given information and the theorems you have learned to show that r || s. 4  8 4  8 r || s

Example : Proving Lines Parallel Given: p || r , 1  3 Prove: ℓ || m

What lines are parallel? Line BG bisects <ABF A B 45 D F 65 70 G H

Lesson Quiz: Part I Name the postulate or theorem that proves p || r. 1. 4  5 Conv. of Alt. Int. s Thm. 2. 2  7 Conv. of Alt. Ext. s Thm. 3. 3  7 Conv. of Corr. s Post. 4. 3 and 5 are supplementary. Conv. of Same-Side Int. s Thm.

Lesson Quiz: Part II Use the theorems and given information to prove p || r. 5. m2 = (5x + 20)°, m 7 = (7x + 8)°, and x = 6 m2 = 5(6) + 20 = 50° m7 = 7(6) + 8 = 50° m2 = m7, so 2 ≅ 7 p || r by the Conv. of Alt. Ext. s Thm.