Mathematics - Junior Secondary 3 - Geometry I

TERM: 2^ND TERM

WEEK 4
Class: Junior Secondary School 3
Age: 14 years
Duration: 40 minutes of 5 periods
Subject: Mathematics
Topic: Geometry I – Similar Shapes
Focus: Identification of Plane Shapes

Specific Objectives:
By the end of the lesson, pupils should be able to:

Identify similar shapes and their properties.
Recognize the criteria for similarity of two shapes.
Identify common shapes like triangles, rectangles, and circles in real life.
Understand the concept of enlargement and scale factor.
Apply knowledge of similar shapes in problem-solving situations.

Instructional Techniques:
• Direct instruction
• Demonstration
• Group discussion
• Problem-solving exercises

Instructional Materials:
• Flashcards with different shapes
• Scale rulers
• Whiteboard and marker
• Examples of similar shapes in everyday life (images, objects)

PERIOD 1 & 2: Identification of Plane Shapes

Presentation:

Step	Teacher’s Activity	Pupil’s Activity
Step 1 – Introduction	Introduces the concept of similar shapes, using simple examples (e.g., two triangles of the same shape but different sizes).	Pupils observe and ask questions.
Step 2 – Explanation	Defines the criteria for similarity: shapes are similar if their corresponding angles are equal and their corresponding sides are proportional.	Pupils write down the definition and ask clarifying questions.
Step 3 – Demonstration	Shows examples of similar and non-similar shapes using diagrams.	Pupils identify shapes and state whether they are similar.
Step 4 – Practice	Provides pupils with various shapes to classify as similar or not.	Pupils work in groups to classify shapes.

Evaluation (5 exercises):

Identify which shapes are similar.
State the criteria for similarity between two triangles.
Check if two rectangles are similar.
Explain why two circles are always similar.
Classify the shapes in the given set.

Classwork (5 questions):

Identify the shapes in your environment that are similar.
Draw two similar triangles and label their corresponding sides.
Draw and label similar rectangles.
Show that two squares are always similar.
Find and compare the areas of two similar shapes.

Assignment (5 tasks):

Identify 5 similar shapes from newspapers or magazines.
List the properties of similar triangles.
Draw a pair of similar polygons and compare them.
Write a short note on the importance of similarity in geometry.
Create a word problem using similar shapes and solve it.

PERIOD 3 & 4: Enlargements and Scale Factor

Presentation:

Step	Teacher’s Activity	Pupil’s Activity
Step 1 – Introduction	Explains the concept of enlargement and scale factor.	Pupils listen and ask questions.
Step 2 – Explanation	Demonstrates how to enlarge shapes using a scale factor.	Pupils observe and practice enlarging shapes.
Step 3 – Practice	Provides exercises to enlarge shapes using different scale factors.	Pupils practice enlarging shapes on paper.
Step 4 - Note Taking	Teacher writes the steps of enlargement and scale factor on the board.	Pupils copy the procedure and practice.

Evaluation (5 exercises):

Enlarge a rectangle with a scale factor of 2.
Enlarge a square with a scale factor of 3.
Use a scale factor of 0.5 to reduce a shape.
Find the area of an enlarged triangle with a scale factor of 4.
Compare two enlarged shapes with different scale factors.

Classwork (5 tasks):

Enlarge the following triangle with a scale factor of 2.
Reduce the following square with a scale factor of 0.5.
Use a scale factor of 3 to enlarge the given shape.
Find the new area after enlarging a shape with a scale factor of 3.
Draw and enlarge a shape by a factor of 5.

Assignment (5 tasks):

Find the new perimeter and area of an enlarged rectangle with a scale factor of 4.
Reduce the given circle with a scale factor of 0.5.
Use a scale factor of 2.5 to enlarge a triangle.
Write the steps involved in enlarging any plane shape.

Create and solve a problem involving enlargements and scale factors.

Mathematics - Junior Secondary 3 - Geometry I - Similar shapes