Download 10 GEOMETRY OF 2D SHAPES Term 2 Lesson 1 Grade 9

MATHEMATICS LESSON PLAN
GRADE 9
TERM 2: APRIL – JUNE 2015
PROVINCE:
DISTRICT:
SCHOOL:
TEACHER’S NAME:
DATE:
DURATION:
1 hour
1. TOPIC: GEOMETRY OF 2D SHAPES: CLASSIFYING 2D SHAPES (Lesson 1)
2. CONCEPTS & SKILLS TO BE ACHIEVED:
By the end of the lesson learners should know and be able to:
 use properties and definitions of triangles in terms of their sides and angles,
distinguishing between:
- equilateral triangles.
- isosceles triangles.
- right-angled triangle.
 solve geometric problems involving unknown sides and angles in triangles.
Grade 9 Lesson Plan: 1+4 Intervention – Term 2
(Draft)
3. RESOURCES:
4. PRIOR KNOWLEDGE:
DBE workbook, Sasol-Inzalo workbook, textbooks, ruler,
protractor, pencil, (mathematical set), calculator

types of triangles

properties of triangles

constructions
5. REVIEW AND CORRECTION OF HOMEWORK (suggested time: 10 minutes)
Homework provides an opportunity for teachers to track learner’s progress in the mastery of
mathematics concepts and to identify the problematic areas which require immediate
attention. Therefore it is recommended that you place more focus on addressing errors from
learner responses that may later become misconceptions.
6. INTRODUCTION (Suggested time: 10 Minutes)
Prepare the following questions on a chart in order to give learners to respond.
1.
2.
3.
4.
5.
6.
The sum of the interior angles of triangles is equal to ________
The equilateral triangle has all sides equal in length and all angles equal to________
An ___________triangle has at least two equal sides and its base angles are equal
A ___________ triangle has one angle that is a right angle
The side opposite the right angle in a right-angled triangle, is called the ___________
In a right-angled triangle, the square of the hypotenuse is equal to the sum of the
______________.
7. LESSON PRESENTATION/DEVELOPMENT (Suggested time: 30 minutes)
Teaching activities
Learning activities
(learners are expected
to: )
Complete the following activities with the learners:
Activity 1



Let learners draw 1 triangle and measure the interior angles
complete the activities
using a protractor.
given by the teacher
Have them add all the interior angles of their triangles and
discuss their answers.
Learners should discover that the sum of the interior angles of
a triangle is equal to 180°
Grade 9 Lesson Plan: 1+4 Intervention – Term 2
(Draft)
Page 2 of 5
a) Determine the size of angle x with reasons:
A
𝑥
50°
43°
B
C
(Expected answer)
𝐴̂ + 𝐵̂ + 𝐶̂ = 180° (sum of angles of a triangle)
𝑥 + 43° + 50° = 180°
𝑥 + 93° = 180°
𝑥 + 93° − 93° = 180° − 93°
𝑥 = 87°
Activity 2

Allow learners to construct any equilateral triangle of any
length.

Let them measure each interior angle and discover that each
angle within an equilateral triangle measures 60°.
a) Calculate the value 𝑥 with reasons:
complete the activities
given by the teacher
A
3𝑥
B
C
Grade 9 Lesson Plan: 1+4 Intervention – Term 2
(Draft)
Page 3 of 5
Activity 3

Allow learners to construct a triangle with 2 sides equal in
length (the triangle must not extend beyond the A4 page).

Let learners measure all interior angles and lead them to
discover that in an isosceles triangle the 2 base angles are
equal.

Calculate the value of 𝑥 and provide reasons:
Q
2𝑥
complete the activities
given by the teacher
50o
R
P
Activity 4

Allow learners to construct any triangle.

Let them extend one of the lengths of the sides by 3cm.

Show learners the exterior angle and the 2 interior
opposite angles.
NB: An exterior angle is the angle between the side of a triangle
and another side that is extended.

Let learners measure the sizes of the interior opposite angles
and the exterior angle using a protractor.

Allow learners to compare and discuss their findings above.
They should discover that the exterior angle of a triangle is
equal to the sum of the two interior opposite angles.
Grade 9 Lesson Plan: 1+4 Intervention – Term 2
(Draft)
Page 4 of 5
D
a
F
a+b
b
G
exterior angle
Complete the activities
given by the teacher

Guide learners to determine the value of 𝑥 with reasons:
86o
𝑥 + 10°
42°
𝑥 + 10° + 42° = 86°
(exterior angle of triangle)
𝑥 + 52° = 86°
𝑥 = 34°
8. CLASSWORK (Suggested time: 20 minutes)
Activity 1







Construct a 90o angle in order to draw a right angled-triangle.
Measure the other 2 angles and the 3 sides of the triangle.
Add all the interior angles of your triangle. What can you conclude?
Calculate the square of the lengths of each of the sides of the triangle.
Add the squares of the lengths of the 2 smaller sides and compare this sum to the
square of the larger side facing the 90° angle.
Make a summary of your findings.
̂ =43°. AB = 8cm,
̂ = 90°, A
In the right-angled triangle given below, not drawn to scale, B
BC = 6𝑐𝑚.
Determine the size of:
a) Angle 𝐶̂
b) The length of AC
A
B
C
Grade 9 Lesson Plan: 1+4 Intervention – Term 2
(Draft)
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