Anglesand their rules

Lesson Objective

Lesson Success Criteria

To learn about angles, in relation to points, lines, triangles, and general polygons

• Can identify different types of angles, and calculate using appropriate geometric reasoning

Geometric Reasoning

The REASON for an answer is the geometric property

not the arithmetic that led to the answer

ALL answers must have a REASON

Geometric Language

Using the correct language is extremely important.

Refer to Geometric Glossary on my website.

Abbreviated form is ok to use but ensure it is correct.

Angle RulesRule Short Version Diagram

1Angles at a point add to 360°

2Adjacent angles on a straight line

add to 180°

3Vertically opposite angles are

equal

PracticeFrom homework book

Page 187 Ex A: Finding unknown angles

Triangle RulesRule Short Version Diagram

4Angle sum of a triangle add to

180°

5

Exterior angles of a triangle equals the sum of the two opposite interior angles

6

Angles in an equilateral triangle are equal (to 60°)

Triangle RulesRule Short Version Diagram

7Base angles in an isosceles

triangle are equal

PracticeFrom homework book

Page 193 Ex C: Triangles

Quadrilaterals - interior angles sum to 360°

QuadrilateralsQuadrilaterals - interior angles sum to 360°

PracticeFrom homework book

Page 195 Ex D: Quadrilaterals

Polygon RulesRule Short Version Diagram

8Exterior angles of a polygon add

to 360°

9

Interior angles of a polygon

- Sum to (n-2) x 180- Equal to 180 – exterior angle

PracticeFrom homework book

Page 197 Ex E: Polygons

Angles and Parallel Lines RulesRule Short Version Diagram

10Corresponding angles between

parallel lines are equal

11Alternate angles between

parallel lines are equal

12Co-interior angles between

parallel lines add to 180°

PracticeFrom homework book

Page 189 Ex B: Angles and Parallel Lines

Complementary Angles

Two angles are called complementary angles if they add to 90°, i.e. a right angle. (they don’t need to be adjacent angles)

Supplementary Angles

Two angles are called supplementary angles if they add to 180°, i.e. a straight line. (they don’t need to be adjacent angles)