# 4th Grade - Right, Acute And Obtuse Angles

 Grade Level: 4th Skill: Shapes and Geometry Topic: Right, Acute and Obtuse Angles Goal: Know definitions of a right angle, and acute angle, and an obtuse angle. Understand that 90anddeg;, 180anddeg;, 270anddeg;, and 360anddeg; are associated, respectively, with andfrac14;, andfrac12;, andfrac34;, and full turns. Skill Description: Know how to identify and measure right, acute, obtuse, and straight angles, using a protractor.

## Building Blocks/Prerequisites

### Sample Problems

 (1) Name the angle: ______________ (obtuse) (2) Name the angle: _______________ (straight) (3) Name the angle: ________________ (Acute) (4) Name the angle that measures 180°: ________________ (straight angle) (5) Identify the angle of the open book: (obtuse)

### Learning Tips

 (1) Math Vocabulary Angle- two rays with the same endpoint Ray- a part of a line that begins with one endpoint and one endless line (no point) Vertex- the point where the two rays meet to make an angle Protractor- a tool used to measure the size of the opening of an angle Acute angle- an angle that has a measure less than 90° Obtuse angle- an angle that has a measure greater than 90°, but less than a straight angle at 180° Straight angle- an angle that measures 180° (straight line) Right angle- an angle that forms a straight corner and measures at 90° (2) Using a Protractor Place the center of the protractor (a dot or hole will be placed on the bottom of the protractor to show its center point) on the vertex of the angle. Line up the 0° measurement line on the bottom ray of the angle. Read the angle measure there the second ray passes through the protractor. Practice measuring angles using a protractor. Make sure the different angles are turned in various positions, so your child will not think the angles are turned in one direction only. Hint: Some children may need to extend the ray that passes through the measurement with a pencil so they can be more accurate when reading the protractor. (3) Use arms to form angles A quick review for angles is to use your arms to make angles. Hold your arms out to the side to make a straight angle, and then move them in various ways to make acute, right, and obtuse angles. Then, call out angles and have your child move his/her arms to form the angles. (4) Use items around the house to identify angles Look at different items in the house and have your child identify the angles. For example, mirrors, doors (slightly open), wall corners, floor tiles, etc. You can make a game: How many items can you find with a right angle in 30 seconds? Have them identify or draw them (outlining the angles). (5) Sort Angles Place different angles on index cards and have your child organize them according to the type of angle (right, obtuse, straight, and acute).

### Extra Help Problems

 (1) Name the angle: ____________ (Acute) (2) Name the angle: ________________ (Obtuse) (3) Name the angle: ________________ (Acute) (4) Name the angle: _________________ (Straight) (5) Name the angle: __________ (Right) (6) Name the angle: _________________ (Obtuse) (7) Measure the angle: _______ (18°) (8) Measure the angle: ___________ (40°) (9) Measure the angle: _______ (140°) (10) Measure the angle: ______ (90°) (11) Measure the angle: _______ (180°) (12) Measure the angle: ________ (135°) (13) Greater or less than a right angle: _________ (Less than-Acute) (14) Greater than or less than a right angle: ___________ (Greater than- Obtuse) (15) Greater than or less than a right angle: _________ (Equal to—Right angle) (16) Name the angle that measures 60°: ________________ (acute angle) (17) Name the angle that measures 90°: ________________ (right angle) (18) Name the angle that measures 179°: ________________ (obtuse angle) (19) Name the angle that measures 14°: ________________ (acute angle) (20) Name the angle that measures 95°: ________________ (obtuse angle) (21) Name the angle that measures 60°: ________________ (acute angle) (22) Identify the angle of the open laptop computer: ____________________ (Acute angle) (23) Identify the angle of the pizza slice: _____________ (Acute angle) (24) Identify the angle of corners of the picture frame: ________________ (Right angle) (25) Identify the angle of the street pole: _________________ (straight angle)