1. In your NOTEBOOK!!! Write the following two puzzles, and try to solve them quietly: Example: He’s/Himself = “He’s beside himself” 1. ANGLE2. LAWMOTHERLAW ANGLE

2. Lesson 4.1 – Triangle Sum

3. Today’s Goal Formally define a triangle and begin finding missing angles! WHY? –Triangles are the only rigid polygon

4. New Material – VOCAB SECTION Triangle A closed figure (polygon) with three sides. ∆ABC Triangle Sum Theorem The sum of the interior angles of a triangle is equal to 180° 1 + 2 + 3 = 180 1 2 3 A B C

5. In your Notes How to find the missing angle –Step 1: Add two given angles. –Step 2: Subtract sum from 180. –Step 3: This is the missing angle. 70° y 60° S1: 60 + 70 = 130 S2: 180 – 130 = 50 S3: y = 50°

6. In your Notes… Copy down the following drawings and identify why it is NOT A TRIANGLE… WARNING: There may not be a problem! i.e. It might be a triangle! 1. 2. 75° 50° 55° Not a closed figure!No problems!

7. 3. 30° 50° 4. 5. 97° 30° 20° 6. 87° 33° 60° Angles don’t add to 180 No Problem! Has 4 sides, not 3 Angles don’t add to 180

8. Problem of the Day What is the value of z in the picture below? A. 32° B. 58° C. 122° D. 180°

9. Homework Lesson 4.1/ 1 – 9 Vocabulary