Class: Junior Secondary School 3 (JSS3, JSS 3)
Term: 1st Term
Week: 5
Age: 14 years
Duration: 45 minutes
Subject: Mathematics
Curriculum Theme: Mathematics
Previous Lesson: Rational and Non-rational Numbers, Approximation and Reciprocals
Topic: Plane Figures
Subject Matter: Problems in mensuration involving: Area of triangles, Area of parallelograms, Area of trapezium, Area of circles and sectors, Word problems involving area.

Specific Objectives

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

Cognitive Domain:
(a) Identify and recall formulas for calculating areas of plane figures.
(b) Solve numerical problems involving the area of triangles, parallelograms, trapeziums, circles, and sectors.
Affective Domain:
(a) Appreciate the usefulness of mensuration in solving real-life problems involving space and measurement.
Psychomotor Domain:
(a) Apply the correct formula to solve given problems on areas of plane figures.
(b) Draw and label simple plane figures correctly for area calculation.
Social Domain:
(a) Work collaboratively in pairs or small groups to solve area-related problems.

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 – “Area of Plane Shapes” (https://www.mathsisfun.com/area.html)
BBC Bitesize – “Area and Perimeter of 2D Shapes” (https://www.bbc.co.uk/bitesize/topics/zjbg87h/articles/zsqxfcw)
Relevant Textbooks

Instructional Materials

The teacher will teach this lesson with the aid of:

Chart showing different plane figures
Mathematical instruments (ruler, compass, protractor)
Graph sheets
Cardboard cut-outs of various plane shapes
Marker and board ruler

Rationale for the Lesson

Mensuration helps students understand how to determine areas of plane figures, which is essential in solving real-life problems involving land measurement, construction, and design.

Prerequisite/Previous Knowledge

Pupils are already familiar with basic geometric shapes, their sides, and properties. They have also learned how to find the perimeter of simple shapes in previous lessons.

Lesson Content/Board Summary

Plane Figures

Area of a Triangle

A triangle is a plane figure with three sides and three angles. The area of a triangle is the amount of surface enclosed by its sides.

The formula for the area of a triangle is:
[
text{Area} = frac{1}{2} times text{base} times text{height}
]

Example 1:
Find the area of a triangle with base 10 cm and height 6 cm.
[
text{Area} = frac{1}{2} times 10 times 6 = 30 text{ cm}^2
]

Area of a Parallelogram

A parallelogram has opposite sides that are equal and parallel. Its area is calculated using the base and height (the perpendicular distance between opposite sides).

The formula is:
[
text{Area} = text{base} times text{height}
]

Example 2:
Find the area of a parallelogram with base 12 cm and height 8 cm.
[
text{Area} = 12 times 8 = 96 text{ cm}^2
]

Area of a Trapezium

A trapezium has one pair of opposite sides parallel. Its area depends on the sum of the parallel sides and the height.

The formula is:
[
text{Area} = frac{1}{2} (text{sum of parallel sides}) times text{height}
]

Example 3:
Find the area of a trapezium with parallel sides 8 cm and 12 cm, and height 5 cm.
[
text{Area} = frac{1}{2} (8 + 12) times 5 = frac{1}{2} times 20 times 5 = 50 text{ cm}^2
]

Area of a Circle

A circle is a plane figure bounded by a curved line called the circumference, and all points are equidistant from the center.

The formula for area is:
[
text{Area} = pi r^2
]

Where ( r ) is the radius of the circle and ( pi = 3.142 ) or ( frac{22}{7} ).

Example 4:
Find the area of a circle with radius 7 cm.
[
text{Area} = frac{22}{7} times 7 times 7 = 154 text{ cm}^2
]

Area of a Sector

A sector is a part of a circle bounded by two radii and an arc. Its area depends on the angle at the center.

The formula is:
[
text{Area of Sector} = frac{theta}{360^circ} times pi r^2
]

Where ( theta ) is the angle at the center.

Example 5:
Find the area of a sector of a circle with radius 6 cm and central angle 90°.
[
text{Area} = frac{90}{360} times 3.142 times 6^2 = frac{1}{4} times 3.142 times 36 = 28.278 text{ cm}^2
]

Teaching Methods/Instructional Techniques:

Discussion, Lecture, Explanation, Demonstration, Question and Answer, Guided Discovery, Problem-Solving

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 asks pupils to mention examples of plane shapes they have seen in their environment (e.g., wall tiles, book covers) and recalls formulas for perimeter.
Pupils’ Activity: Pupils respond by naming shapes and recalling perimeters.
Learning Point: Pupils recall basic geometric shapes and relate them to real-life examples.

Step 2: Area of Triangles and Parallelograms

Time: 10 minutes
Teaching Skill: Explanation
Teacher’s Activity: The teacher explains and derives the formula for area of a triangle and parallelogram using diagrams on the board.
Pupils’ Activity: Pupils observe, take notes, and solve one guided example.
Learning Point: Pupils understand and apply formulas for finding area of triangles and parallelograms.

Step 3: Area of Trapezium and Circle

Time: 10 minutes
Teaching Skill: Demonstration
Teacher’s Activity: Teacher uses cut-out shapes to show the trapezium and circle, explains formulas, and works through sample problems.
Pupils’ Activity: Pupils watch demonstration and calculate in pairs.
Learning Point: Pupils correctly apply area formulas for trapezium and circle.

Step 4: Area of Sector and Word Problems

Time: 10 minutes
Teaching Skill: Guided Discovery
Teacher’s Activity: Teacher explains sector area using a chart of a circle, then provides real-life word problems for pupils to solve.
Pupils’ Activity: Pupils solve given problems and present answers.
Learning Point: Pupils can solve problems involving sector area and practical applications.

Step 5: Note-Taking

Time: 5 minutes
Teaching Skill: Reinforcement
Teacher’s Activity: Teacher dictates or writes the summarized lesson content for pupils to copy.
Pupils’ Activity: Pupils copy notes into their exercise books.
Learning Point: Pupils have accurate notes of formulas and examples.

Step 6: Evaluation/Review

Time: 3 minutes
Teaching Skill: Questioning
Teacher’s Activity: The teacher evaluates the learning by asking the following questions:

State the formula for the area of a triangle.
Calculate the area of a trapezium with sides 10 cm and 6 cm, and height 5 cm.
Find the area of a circle of radius 3 cm.
What is the area of a sector with radius 8 cm and angle 120°?
Pupils’ Activity: Pupils answer orally and on the board.
Learning Point: Pupils demonstrate mastery of area calculations.

Step 7: Conclusion

Time: 2 minutes
Teaching Skill: Reinforcement
Teacher’s Activity: Teacher summarizes key points and encourages pupils to practice more area problems at home.
Pupils’ Activity: Pupils listen and ask clarifying questions.
Learning Point: Pupils are motivated to apply area knowledge to real-life problems.

Lesson Keywords

Triangle – a shape with three sides and three angles
Parallelogram – a four-sided figure with opposite sides parallel
Trapezium – a four-sided figure with one pair of parallel sides
Circle – a shape with all points equidistant from a center
Sector – part of a circle bounded by two radii and an arc

Differentiation

Provide extra guidance and visual aids for slower learners, while faster learners handle more complex word problems independently.

Note for teachers using this lesson plan

Ensure pupils memorize and apply all formulas correctly. Reinforce learning with real-world examples such as land areas and design measurements.