1. Holt CA Course 1 9-2 Measuring and Classifying Angles Warm Up Warm Up Lesson Presentation California Standards Preview

2. Holt CA Course 1 9-2 Measuring and Classifying Angles Warm Up 1. Draw two points. Label one point A and the other point B. 2. Draw a line through points A and B. 3. Draw a ray with A as an endpoint and C as a point on the ray. 4. Name all the rays in your drawing. AB, BA, and AC AB C

3. Holt CA Course 1 9-2 Measuring and Classifying Angles Preparation for MG2.1 Identify angles as vertical, adjacent, complementary, or supplementary and provide descriptions of these terms. Also covered: Prep for MG2.3 California Standards

4. Holt CA Course 1 9-2 Measuring and Classifying Angles An angle is formed by two rays with a common endpoint, called the vertex. An angle can be named by its vertex or by its vertex and a point from each ray. The middle point in the name should always be the vertex. Angles are measured in degrees. Use the symbol ° to show degrees.

5. Holt CA Course 1 9-2 Measuring and Classifying Angles mFGH is read “the measure of angle FGH.” Reading Math

6. Holt CA Course 1 9-2 Measuring and Classifying Angles An acute angle measures less than 90°. A right angle measures exactly 90°. Right angles are usually marked with a symbol. Reading Math

7. Holt CA Course 1 9-2 Measuring and Classifying Angles An obtuse angle measures more than 90° and less than 180°. A straight angle measures exactly 180°.

8. Holt CA Course 1 9-2 Measuring and Classifying Angles Vocabulary angle vertex acute angle right angle obtuse angle straight angle

9. Holt CA Course 1 9-2 Measuring and Classifying Angles Additional Example 1: Measuring an Angle with a Protractor Use a protractor to measure the angle. Place the center point of the protractor on the vertex of the angle. G H F

10. Holt CA Course 1 9-2 Measuring and Classifying Angles Additional Example 1 Continued Use a protractor to measure the angle. Place the protractor so that ray GH passes through the 0° mark. G H F

11. Holt CA Course 1 9-2 Measuring and Classifying Angles Using the scale that starts with 0° along ray GH, read the measure where ray GF crosses. Additional Example 1 Continued Use a protractor to measure the angle. G H F

12. Holt CA Course 1 9-2 Measuring and Classifying Angles The measure of FGH is 120°. Write this as mFGH = 120°. Additional Example 1 Continued Use a protractor to measure the angle. G H F

13. Holt CA Course 1 9-2 Measuring and Classifying Angles Additional Example 2: Drawing an Angle with a Protractor Use a protractor to draw an angle that measures 80°. Draw a ray on a sheet of paper.

14. Holt CA Course 1 9-2 Measuring and Classifying Angles Additional Example 2 Continued Use a protractor to draw an angle that measures 80°. Place the center point of the protractor on the endpoint of the ray. Place the protractor so that the ray passes through the 0° mark.

15. Holt CA Course 1 9-2 Measuring and Classifying Angles Additional Example 2 Continued Use a protractor to draw an angle that measures 80°. Make a mark at 80° above the scale on the protractor. Use a straightedge to draw a ray from the endpoint of the first ray through the mark you made at 80°.

16. Holt CA Course 1 9-2 Measuring and Classifying Angles Additional Example 3: Classifying Angles Classify each angle as acute, right, obtuse, or straight. A.B. The angle measures less than 90°, so it is an acute angle. The angle measures exactly 90°, so it is a right angle.

17. Holt CA Course 1 9-2 Measuring and Classifying Angles Additional Example 4: Application A welder used this piece of metal on his project. Classify X, Y, and Z. X right Y obtuse Z acute The angle is marked as a right angle. The angle measures more than 90° and less than 180°. The angle measures less than 90°.

18. Holt CA Course 1 9-2 Measuring and Classifying Angles Check It Out! Example 1 Use a protractor to measure the angle. H I G Place the center point of the protractor on the vertex of the angle.

19. Holt CA Course 1 9-2 Measuring and Classifying Angles Check It Out! Example 1 Continued Use a protractor to measure the angle. Place the protractor so that ray HI passes through the 0° mark. H I G

20. Holt CA Course 1 9-2 Measuring and Classifying Angles Check It Out! Example 1 Continued Use a protractor to measure the angle. H I G Using the scale that starts with 0° along ray HI, read the measure where ray HG crosses.

21. Holt CA Course 1 9-2 Measuring and Classifying Angles Check It Out! Example 1 Continued Use a protractor to measure the angle. H I G The measure of GHI is 70°. Write this as mGHI = 70°.

22. Holt CA Course 1 9-2 Measuring and Classifying Angles Check It Out! Example 2 Use a protractor to draw an angle that measures 45°. Draw a ray on a sheet of paper.

23. Holt CA Course 1 9-2 Measuring and Classifying Angles Place the center point of the protractor on the endpoint of the ray. Place the protractor so that the ray passes through the 0° mark. Check It Out! Example 2 Continued Use a protractor to draw an angle that measures 45°.

24. Holt CA Course 1 9-2 Measuring and Classifying Angles Make a mark at 45° above the scale on the protractor. Use a straightedge to draw a ray from the endpoint of the first ray through the mark you made at 45°. Check It Out! Example 2 Continued Use a protractor to draw an angle that measures 45°.

25. Holt CA Course 1 9-2 Measuring and Classifying Angles Check It Out! Example 3 Classify each angle as acute, right, obtuse, or straight. A.B. The angle measures less than 90°, so it is an acute angle. The angle measures exactly 180°, so it is a straight angle.

26. Holt CA Course 1 9-2 Measuring and Classifying Angles Check It Out! Example 4 A metal jeweler used this piece of metal on her project. Classify A,  B, and  D. D C A B A obtuse B acute  D rightThe angle is marked as a right angle. The angle measures more than 90° and less than 180°. The angle measures less than 90°.

27. Holt CA Course 1 9-2 Measuring and Classifying Angles Lesson Quiz Use a protractor to draw an angle with the given measure. Tell what type of angle it is. 1. 140° 2. 20° 3. Draw a right angle. 4. Is the angle shown closer to 30° or 120°? Check student drawings: acute Check student drawings; obtuse 30°