1. CCSS: G.CO.9 Prove theorems about lines and angles.
Date:
5.4(a) Notes: The Angle Addition Postulate, Supplementary and Complementary Angles
Lesson Objective: Discover the angle addition postulate. Write proofs involving supplementary and complementary angles.
CCSS: G.CO.9 Prove theorems about lines and angles.

2. Lesson 1: Angle Addition Postulate
Draw / ABC with a measure of 125°. • •

3. Lesson 1: Angle Addition Postulate
Draw / ABC with a measure of 125°. • B C A

4. Draw / DBC with a measure of 45°.
What is the measure of / ABD? • B C A D

5. Angle Addition Postulate:
D is in the interior of / ABC if and only if
m/ ABD + m/ DBC = m/ ABC • • A D B C

6. Lesson 2: Use the Angle Addition Postulate
If m/ 1 = 23° and m/ ABC = 131°, find m/ 3. Justify each step.

7. Lesson 3: Supplement Theorem
Draw a line across the page about 4 blue lines down. Use your protractor to measure the line. _______

8. Lesson 3: Supplement Theorem
Draw a line across the page below. Use your protractor to measure the line. 180°
Draw / 1 with a measure of 50°.
What is m/ 2? ______
What is m/ 1 + m/ 2? ______
50°

9. Supplement Theorem:
If 2 angles form a linear pair, then they are supplementary angles (they add up to 180°).
Linear Pair: A pair of adjacent angles with noncommon sides that are opposite rays (they add up to 180°).
Example: m/ 1 + m/ 2 = 180°

10. Lesson 4: Using the Supplement Theorem
/ 6 and / 7 form linear pair. If m/ 6 = 3x + 32 and m/ 7 = 5x + 12, find x, m/ 6, and m/ 7. Justify each step.