1. Chapter 20
Angles

2. Objectives Names of Angles Measuring Angles Drawing Angles
Angles at a Point
Complimentary Angles
Supplementary Angles
Parallel Lines & Angles
Compass Points
Bearings – Reading & Drawing
Scale Diagrams

3. Types & Names Acute – less than 90o Right angle – 90o
Obtuse – between 90o and 180o
Straight line – 180o
Reflex – between 180o and 360o
Complete turn - 360o

4. Angle Rules Angles at a point add to 360o
Complementary angles add to 90o
Supplementary angles add to 180o
Vertically opposite angles are equal

5. Examples 1. 3. 5. 2. 4. 6.

6. Parallel Lines Parallel lines never meet
Corresponding angles are equal
Alternate angles are equal
Interior angles add to 180o

7. Examples 1. 3. 2. 4.

8. Naming Angles Use 3 letters with the middle letter at the angle point
Examples

9. Direction & Compass Points

10. Bearings All bearings must have 3 figures
All bearings are measured clockwise from North

11. Back Bearings
Examples

12. Scale Drawings
If units are not denoted they are assumed to be the same
Eg 1:10 000
Eg 1cm to 10 km

13. Examples
A plan of a boat is 1:65. If the width on the plan is 20 cm, what is the actual length?
The scale on a map is 1:200. A field is 60m long. What is it’s width on the map?

14. Drawing Scale Drawings
Example
A boat sails on a course of 040o for 5km and then a further 3km on a bearing of 120o. Find by scale drawing
The distance the boat is from the starting point.
The bearing on which it must return
to sail directly back to the start