Возрастная группа: 4 t h Grade, 5 t h Grade Virginia - Mathematics Standards of Learning (2009): 5.11, 5.12a,

Transcription

1 1 План урока Measuring Angles Acute, Right, Obtuse Возрастная группа: 4 t h Grade, 5 t h Grade Virginia - Mathematics Standards of Learning (2009): 5.11, 5.12a, 5.12b Virginia - Mathematics Standards of Learning (2016): 5.12, 5.13.b Fairfax County Public Schools Program of Studies: 5.11.a.1, 5.11.a.2, 5.12.a.1, 5.12.b.1, 5.12.b.2 Онлайн ресурсы: P ro t rac t o r Opening Teacher present s Students pract ice Class discussion Closing M at h Obj ect ives E xpe ri e nc e using a protractor P rac t i c e measuring angles Learn about angles within triangles De vel o p measurement skills Ope ni ng 8

2 2 Say: Today we are going to talk about angles. Draw the following table on the board: On cards, draw more angles: Ask students to place each piece of cardstock in the appropriate column of the table. Once all cardstock is properly located, discuss the angles. Ask: What are the differences in the three columns? Right a ngle s are angles like the ones in the corner of a piece of paper. A c ut e a ngle s are smaller than right angles. Obt us e a ngle s are larger than right angles.

3 3 Ask: How did we determine where to place the angles in the table? We look at the angle. Is it a right angle? If not, is it larger or smaller? Once we know, we will be able to determine which column to place it in. Write on the board: When two lines cross to make four equal angles, those are right a ngle s. Angles that are smaller than right angles are called a c ut e a ngle s. Angles that are larger than right angles are called o bt us e a ngle s. A right angle measures 90 degrees. An acute angle is less than 90 degrees. An obtuse angle is larger than 90 degrees (but smaller than 180). T e ac he r prese nt s M at h game : P ro t rac t o r - Angl e s o f T ri angl e s: Level I 12 Using Preset mode, present Matific s episode Pro t ra c t o r - A ngle s o f T ria ngle s : L e v e l I to the class, using the projector. This episode enables students to practice the use of a protractor to measure angles. Find the size of angles in triangles. Example :

4 4 Ask: What is the name of the tool used to measure angles? It is called a protractor. Say: There are two sets of numbers on a protractor, an inner scale and an outer scale. How do we know which one to use? Responses may vary. Two possible responses: 1. If the angle opens to the right, use the outer scale. If the angle opens to the left, use the inner scale. 2. Determine if the angle is acute, obtuse, or right. Right angles always measure 90 degrees. Look at the two possible angle measures on the protractor. Choose the larger number for obtuse angles and the smaller number for acute angles. Say: Here we are measuring an acute angle. What is the size of the angle? Students should be able to measure the angle using the protractor. Click on the to enter the number that the students offer.

5 5 Click on. If the answer is correct, the episode will proceed to a new problem. If the answer is incorrect, the instructions will wiggle. In the next problem, you will be asked to measure an angle, but the protractor is not in place. You will need to place it properly. Ask: Where do we place the protractor to measure the angle? First, place the origin of the protractor over the vert e x of the angle. Then align the baseline of the protractor with one of the rays of the angle. Use the other ray to find the measurement of the angle. Example :

6 6 Move the protractor as the students suggest. Use the to rotate the protractor. Play a little with the protractor. Finally, place the origin of the protractor over the v e rt e x of angle A. Then align the baseline of the protractor with one of the ra y s of the angle. Ask: Is angle A acute or obtuse? Students can answer based on the angle presented. Ask: What is the angle s measure? Read the measurement from the protractor. Angle A measures 20 degrees.

7 7 St ude nt s prac t i c e M at h game : P ro t rac t o r - Angl e s o f T ri angl e s: Level I 12 Have students play Pro t ra c t o r - A ngle s o f T ria ngle s : L e v e l I on their personal devices. Circulate among the students, answering questions as necessary. Advanced students can move on to play Pro t ra c t o r - A ngle s o f T ria ngle s : L e v e l I I. Cl ass di sc ussi o n 8 Say: In this episode, we measured angles that already exist. Now you will draw angles of a given size. Hand out protractors and worksheets containing the following problems. 1. One ray of an angle is given. Place the origin of your protractor on the endpoint of the ray. Use your protractor to draw another ray to get to the indicated angle. a. 50 degrees b. 25 degrees c. 75 degrees

8 8 d. 150 degrees 2. Now draw the whole angle by yourself so that it has the stated measurement. (First, draw a horizontal ray. Second, look at the measurement listed. Third, set up your protractor on the endpoint of the ray you have just drawn to draw the second ray.) a. 90 degrees b. 30 degrees c. 120 degrees d. 100 degrees Circulate, checking students work. Cl o si ng 5 Give the students the following assignment: 1. Use your protractor to draw an angle. 2. Remember its measurement. 3. Exchange papers with a partner. 4. Measure your partner's angle. 5. Did you arrive at the same measurement?