1. Section/Lesson: Angles
Acute
Obtuse
Right Angle

2. Objectives
By the end of this section/lesson, students should be able to:
Recognise, name and compare angles (e.g: acute and right-angle)
Measure angles with the help of a protractor.

3. Angle in Real Life
Example 1:

4. Angle in Real Life Example 2: arm Base line Acute Angle
Note: Refer to page 91 of book Mathematics Extended Programme Grade 7

5. Angle in Real Life Example 3: Right Angle
Note: Refer to page 91 of book Mathematics Extended Programme Grade 7

6. Angle in Real Life Example 4: Obtuse Angle
Note: Refer to page 91 of book Mathematics Extended Programme Grade 7

7. Comparing Angles
Note: Refer to page 91 of book Mathematics Extended Programme Grade 7

8. Activity 1: Angle Maker
Note: Students are allowed to construct the angle maker from materials given. Teacher to guide.

9. Activity 1: Angle Maker
Introduction of the angle maker (what do the arms represent, use of the instrument)
Step 1
Allow students to open the angle maker and discover the different turn that can be formed between two lines.
Step 2
Step 3
Relate turn to angle.
Step 4
Introduce Measurement of Angle through the protractor.
Note: Teacher support students to open the angle maker and form different angles.

10. Activity 2: Discovering the right angle.
Note: Refer to page 90 of textbook Mathematics Extended- Grade 7

11. Labelling Angles arm angle a vertex a Base line arm Note:
An angle is formed when two lines meet.
The two lines meet at a point called a vertex.
An arc is usually used to represent the angle.
We can label the angle by a letter of the alphabet (e.g. a, b, c, ….)

12. Comparison Measure length Measure angle Ruler Protactor
Units used : mm, cm
Units used : degrees

13. Let’s Measure Some Angles.
Now that you know the Right angles, acute angles, and obtuse angles, we are going to learn to measure them. Angles are measured in degrees. But these degrees have nothing to do with the temperature. To measure an angle in degrees, we use a tool called a protractor. Here is a picture of a protractor.
To measure angles, we use a Protractor

14. A Right Angle is 90°
Protractors are usually made of clear plastic so that you can see right through them. You just lay the protractor on top of the angle that you wish to measure. Here’s our old friend, the right angle. The bottom line is directly over the zero. We get our reading from the tall line. It is right over the 90 degree line, isn’t it. So remember this- A right angle is 90 degrees.

15. An Acute Angle is less than 90°
Here’s an acute angle. Do you see how we line up the tip of the angle with the center of the protractor? The bottom line is still directly over the zero. How many degrees is this angle? An acute angle is less than 90 degrees.

16. Here are more acute angles- both less than 90 degrees.
Here are two more acute angles. One is much smaller than the other, but as long as they are less than 90 degrees which is the size of the right angle, they are acute.

17. An Obtuse Angle is more than 90°
Here’s an obtuse angle. It is more than 90 degrees. It’s a bigger angle than the right angle.

18. Here are more obtuse angles- both more than 90 degrees.
Here are two more acute angles. One is much smaller than the other, but as long as they are less than 90 degrees which is the size of the right angle, they are acute.

19. Activity 3: Measuring angles
Note: Students are provided with protractors (or they can have their own) and asked to measure the angles formed between two intersecting

20. Multiple Choice/ sorting
Question 1: Select the right answer.
An acute angle is _______________ a right angle.
equal to
less than
greater than

21. Multiple Choice/ sorting
(b) An obtuse angle is ______________a right angle.
equal to
greater than
less than

22. Multiple Choice/ sorting

23. Multiple Choice/ sorting

24. Multiple Choice/ sorting

25. Multiple Choice/ sorting
If you know the angle measures more than 90 degrees, then
what type of angle is it called?
A straight
B acute
C obtuse
D right

26. Sort the angles into the correct box
right
straight
acute
obtuse
159o
64o
59o
90o
124o
90o o 21
180o
25o
Note: Now, escape the slide show and then drag the diagrams to the correct box.

27. Multiple Choice/ sorting
Question 3: Which one of the following diagrams is incorrect? B.
117˚ A.
100˚ C.
90˚ D.
180˚

28. Homework:
Find the different types of angles in your surroundings and classify them as acute, obtuse, straight or right. Find three types of each and fill in the chart.
Acute
Right
Obtuse
Straight

29. End of Lesson
Thank you. 