Class: Junior Secondary School 2 (JSS2, JSS 2)
Term: 1st Term
Week: 8
Age: 13 years
Duration: 45 minutes
Subject: Basic Science And Technology
Curriculum Theme: Basic Technology
Previous Lesson: Bisection of Angles and Construction of 90°, 60°, 45°, 30°, and 15°
Topic: Triangles (Part 1)
Subject Matter: Definition And Types Of Triangles

Specific Objectives

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

Cognitive Domain:
(a) Define a triangle.
(b) Identify and classify different types of triangles.
Affective Domain:
(a) Appreciate the importance of triangles in construction and design.
Psychomotor Domain:
(a) Draw and label different types of triangles correctly.
Social Domain:
(a) Work cooperatively in groups to discuss and sketch triangles.

Reference Materials

The following resources was used in planning this lesson:

9 Years Basic Education Curriculum
Lagos State Unified Scheme of work for Junior Secondary Schools
Math is Fun – “Types of Triangles” (https://www.mathsisfun.com/triangle.html)
Relevant Textbooks

Instructional Materials

The teacher will teach this lesson with the aid of:

Geometrical sets (compass, protractor, ruler, pencil, eraser)
Drawing charts showing different types of triangles
Flash cards with triangle shapes
Whiteboard and marker
Multimedia projector (if available)

Rationale for the Lesson

Understanding triangles is essential in geometry and practical design because they are the simplest polygons and are widely used in engineering, construction, and art.

Prerequisite/Previous Knowledge

Pupils are already familiar with basic shapes such as squares, rectangles, and circles, and they can identify sides and angles of simple figures.

Lesson Content/Board Summary

Triangles

Definition of a Triangle

A triangle is a closed plane figure formed by three straight lines joining three points. It has three sides, three angles, and three vertices.

Types of Triangles by Sides

Triangles can be grouped according to the length of their sides.

The following are the types of triangles by sides:

Equilateral Triangle – all three sides are equal in length, and all angles are 60°.
Isosceles Triangle – two sides are equal in length, and the angles opposite them are equal.
Scalene Triangle – all three sides are of different lengths, and all angles are unequal.

Types of Triangles by Angles

Triangles can also be classified according to their angles.

The following are the types of triangles by angles:

Acute-angled Triangle – all three angles are less than 90°.
Right-angled Triangle – one of the angles is exactly 90°.
Obtuse-angled Triangle – one of the angles is greater than 90°.

Teaching Methods/Instructional Techniques:

Discussion, Lecture, Explanation, Demonstration, Question and Answer, Group Work, Use of Visual Aids

Instructional Procedures

To deliver this lesson, the teacher will adopt the following steps:

Step 1: Introduction

Time: 5 minutes
Teaching Skill: Set Induction
Teacher’s Activity: Teacher shows a chart of different shapes and asks pupils to identify those with three sides.
Pupils’ Activity: Pupils respond by naming triangles and recalling their previous knowledge of shapes.
Learning Point: Pupils become curious and prepared to learn about triangles.

Step 2: Definition of a Triangle

Time: 7 minutes
Teaching Skill: Explanation
Teacher’s Activity: Teacher defines a triangle and explains its parts (sides, angles, vertices) using a diagram.
Pupils’ Activity: Pupils observe, listen, and draw a triangle in their notebooks.
Learning Point: Pupils understand what a triangle is and its basic features.

Step 3: Types of Triangles by Sides

Time: 10 minutes
Teaching Skill: Demonstration
Teacher’s Activity: Teacher presents diagrams and explains equilateral, isosceles, and scalene triangles.
Pupils’ Activity: Pupils sketch and label each type of triangle.
Learning Point: Pupils learn how to identify triangles by the length of their sides.

Step 4: Types of Triangles by Angles

Time: 10 minutes
Teaching Skill: Discussion
Teacher’s Activity: Teacher explains acute, right, and obtuse-angled triangles using charts and examples from daily life.
Pupils’ Activity: Pupils draw and label each type of triangle in their notebooks.
Learning Point: Pupils understand how triangles are classified by angles.

Step 5: Note-Taking

Time: 5 minutes
Teaching Skill: Explanation
Teacher’s Activity: Teacher dictates or writes the board summary for pupils to copy.
Pupils’ Activity: Pupils write notes into their exercise books.
Learning Point: Pupils have accurate notes for reference.

Step 6: Evaluation/Review

Time: 5 minutes
Teaching Skill: Questioning
Teacher’s Activity: The teacher evaluates the learning by asking the following questions:

Define a triangle.
Mention and describe the three types of triangles by sides.
Mention and describe the three types of triangles by angles.
Pupils’ Activity: Pupils respond orally to the questions.
Learning Point: Pupils demonstrate their understanding of triangles and their types.

Step 7: Conclusion

Time: 3 minutes
Teaching Skill: Reinforcement
Teacher’s Activity: Teacher summarizes the lesson, highlights key points, and explains that further study will explore properties of triangles.
Pupils’ Activity: Pupils listen and ask questions where necessary.
Learning Point: Pupils are motivated to study more about triangles.

Lesson Keywords

Triangle – a three-sided polygon
Equilateral – having all sides equal
Isosceles – having two equal sides
Scalene – having all sides unequal
Acute – an angle less than 90°
Right angle – an angle of 90°
Obtuse – an angle greater than 90°

Differentiation

Slower learners will be guided with step-by-step drawing while advanced learners may be asked to construct triangles using rulers and protractors.

Note for teachers using this lesson plan

Always use clear diagrams and practical drawing to illustrate triangles. Encourage active participation by allowing pupils to construct and classify triangles themselves.