1. What do we use to measure the angle? PROTRACTOR Angles, Measuring Angles The unit of measurement of an angle is degrees. We measure angles in degrees. 90 degrees is written as 90 0.

2. Zero line or base line Center or origin Angles, Measuring Angles Parts of Protractor Scale

3. Angles, Measuring Angles The scale at the outside is called outer scale. Scale of Protractor The scale at the inside is called inner scale. 0 0 of outer scale 0 0 of inner scale You can measure an angle using the outer or inner scale depending where you put the arm. What is the arm?

4. Angles, Measuring Angles Line A Scale of Protractor arm The line that you will place on the base line or zero line of the protractor is called the arm.

5. Angles, Measuring Angles Line A Scale of Protractor arm The line that you will place on the base line or zero line of the protractor is called the arm.

6. Angles, Measuring Angles Line A Why not 120 0 ? Because the 0 0 of the inner scale lies on Line A or the arm. Scale of Protractor 60 0 Start counting at 0 O from the arm. It can be 0 o of the inner scale or outer scale. arm How wide is the angle?

7. 60 0 Angles, Measuring Angles Line B Why not 120 0 ? Because the 0 0 of the outer scale lies on Line B or the arm. Scale of Protractor Start counting at 0 O from the arm. It can be 0 o of the inner scale or outer scale. arm How wide is the angle?

8. Measuring an angle A B C vertex 1 st step: place the zero line or base line of the protractor on one side of the angle or the arm. 2 nd step: place the center at the vertex of the angle. 70 o Angles, Measuring Angles 3 rd step: read off the outer scale. Example 1 arm

9. Measuring an angle A B C vertex 70 o Angles, Measuring Angles Example 1 Why 70 0 ? Start reading arm

10. Measuring an angle A B C vertex Angles, Measuring Angles Example 1 Start reading Why 70 0 ? arm

11. Measuring an angle A B C vertex 70 o Angles, Measuring Angles Example 1 End reading Why 70 0 ? arm

12. A B C vertex 60 o Measuring an angle 1 st step: place the zero line or base line of the protractor on one side of the angle or the arm. 2 nd step: place the center at the vertex of the angle. Angles, Measuring Angles 3 rd step: read off the inner scale. Example 2 arm

13. A B C vertex Measuring an angle Angles, Measuring Angles Example 2 Why 60 0 ? Start reading arm

14. A B C vertex Measuring an angle Angles, Measuring Angles Example 2 Why 60 0 ? Start reading arm

15. A B C vertex Measuring an angle Angles, Measuring Angles Example 2 Why 60 0 ? End reading arm 60 o

16. Measuring an angle A B C vertex 1 st step: place the zero line or base line of the protractor on one side of the angle or the arm. 2 nd step: place the center at the vertex of the angle. 70 o Angles, Measuring Angles 3 rd step: read off the inner scale. Example 1, alternative arm

17. A B C vertex 60 o Measuring an angle 1 st step: place the zero line or base line of the protractor on one side of the angle or the arm. 2 nd step: place the center at the vertex of the angle. Angles, Measuring Angles 3 rd step: read off the outer scale. Example 2, alternative arm

18. R = R 80 o S = 67 o S W W = 31 o Measuring an angle Angles, Measuring Angles Example 3