Holt CA Course Measuring and Classifying Angles Warm Up Warm Up Lesson Presentation California Standards Preview

Holt CA Course 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

Holt CA Course 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

Holt CA Course 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.

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

Holt CA Course 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

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

Holt CA Course Measuring and Classifying Angles Vocabulary angle vertex acute angle right angle obtuse angle straight angle

Holt CA Course 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

Holt CA Course 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

Holt CA Course 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

Holt CA Course 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

Holt CA Course 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.

Holt CA Course 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.

Holt CA Course 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°.

Holt CA Course 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.

Holt CA Course 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°.

Holt CA Course 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.

Holt CA Course 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

Holt CA Course 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.

Holt CA Course 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°.

Holt CA Course 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.

Holt CA Course 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°.

Holt CA Course 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°.

Holt CA Course 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.

Holt CA Course 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°.

Holt CA Course Measuring and Classifying Angles Lesson Quiz Use a protractor to draw an angle with the given measure. Tell what type of angle it is ° 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°