Chapter 7

Angles &

Parallel Lines

By the end of the lesson, you should be able to :

• Identify different types of angle

• Explore the properties of angles– Complementary– Supplementary– Adjacent angles on a straight line– Angles at a point– Vertically opposite angles

• Interior and Exterior Angles

• Explore the properties of angles formed by parallel lines and transversals– Interior angles– Corresponding angles– Alternate angles

• Use the properties of angles to find unknown angles in a diagram.

Types of Angles

Acute Angles (angle < 90°)

Right Angle (angle = 90°)

Obtuse angle (90°< angle <180°)

Reflex angle (angle >180°)

Types of Angles

20°

70° 60°

30°

Complementary Angles( sum of angles = 90°)

Supplementary Angles(sum of angles = 180°)

120°60°70°

110°

Types of AnglesAdjacent angles

Non - adjacent angles

Common vertex Common Side

Properties of Angles

The sum of adjacent angles on a straight

line is 180° . (Adj. s on a str. Line)

ab c

d

a + b + c + d = 180°

The sum of all angles at a point is 360°

( s at a pt)

a + b + c + d = 360°

Vertically Opposite Angles

ab

cdA B

E

F

a = b =c d

AB and FE are straight lines

Interior and Exterior Angles

These are interior angles formed by adjacent sides

Interior and Exterior Angles

These are exterior angles formed by the extension of an adjacent side

homework

To be done on foolscap. Please draw the diagrams.

Exercise 7.2 (Page 15)

Questions : 5, 7, 8c,d,

9c,d,e,f, 11 all, 19-21

Non-Parallel Line

Parallel Lines

Transversal

Properties of Angles

formed by parallel lines and transversals

2) Corresponding Angles

ab

cd

e f

gh

A B

C D

E

F ONLY when AB // CD

a = e b = f d = h c = g

3) Alternate Angles

cd

e f

A B

C D

E

FONLY when AB // CD

d = f c = e

4) Interior Angles

cd

e f

A B

C D

E

F

e + d = 1800 c + f = 1800

ONLY when AB // CD

homework

To be done on foolscap. Please draw

the diagrams

Exercise 7.3 (Page 25)

Questions : 1c,d,e,f, 2c,d,e,f

3c,d, 4 all, 6