MATHEMATICS GRADE 9
MATHEMATICS GRADE 9
DATE: ..............................................
TOPIC: GEOMETRY OF STRAIGHT LINES
CONCEPTS & SKILLS TO BE ACHIEVED: By the end of the lesson learners should know and be able to write clear descriptions of the
relationship between angles formed: perpendicular lines Intersecting lines
RESOURCES: ONLINE RESOURCES
DBE Workbook 1, Sasol-Inzalo book 1, Textbooks,
INTRODUCTION Revision on the concept from Grade 8: Fundamentals:
What is an angle? This is when two sides (arms) meet at a common point (vertex) or rotate/diverge from a common point.
Parts of an angle The common point is called the vertex And the two straight sides are called arms.
Grade 9 GEOMETRY OF STRAIGHT LINES:
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DAY 1: ACTIVITY 1&2
LESSON PRESENTATION/DEVELOPMENT
Teaching activities
Learning activities (Learners are expected to)
Labelling Angles
There are two main ways to label angles:
1. give the angle a name, usually a lower-case letter like , or sometimes a Greek letter like () or (), , etc. Or
2 by using the three letters on the shape that define the angle, with the middle letter being where the angle is (its vertex).
Example
A
Vertex A
A
C
Vertex C
C
B B
A
Vertex A: Vertex B: Vertex C:
A^ ; BA^ C ; CA^ B ; x B^ ; AB^ C ; CB^ A ; y C^ ; AC^ B ; BC^ A ; z
C Vertex B
B
Grade 9 GEOMETRY OF STRAIGHT LINES:
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Work through the following activity: Activity 1 1.1 Use the marked angles to complete the statements below:
The angles can be labelled as: 1 ... ... . . ... (... . . . ... . + 2) 1 and 2 are called ......1.1.3 ......... angles because they have the same vertex ....1.1.4......, a common arm AC and lie on opposite side of AC.
Grade 9 GEOMETRY OF STRAIGHT LINES:
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Activity 2 Types of angles: Complete the table below by providing the missing information
Name Acute angle
2.2
Obtuse angle Straight line
Diagram A
O
B
2.3
Description 2.1
The square on the
diagram is the symbol to
indicate 90?.
We say that AO is
perpendicular to OB and
we write this as AO OB ,
where
is the symbol
for perpendicular (90?).
Between 90? and 180?
2.4
Reflex angle 2.6
2.5 O
Between 180? and 360
OB rotate until it is on top A/B of OA
The angle is equal to 360?
CONSOLIDATION/CONCLUSION Emphasise the following
Where two lines meet or cross, they form an angle. The point where the two arms (lines) meet is called the vertex. An angle is an amount of rotation. One of the units to measure angles is degrees. P
There are two main ways to label angles:
1. give the angle a name, usually a lower-case letter like , or sometimes a Greek letter like () or (), , etc. Or
2 by using the three letters on the shape that define the angle, with the middle letter being where the angle is (its vertex).
Grade 9 GEOMETRY OF STRAIGHT LINES:
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MEMORANDUM: DAY 1: Activity 1 & 2
1.1.1 2 1.1.2 1
1.1.3 adjacent
1.1.4
Activity 2 2.1 Between 0? and 90? 2.2 Right angle 2.3
2.4 Equal to 180? 2.5
2.6 Revolution
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