# Area of Triangles (Primary 5)

Last Updated on July 16, 2020 by Alabi M. S.

**MATHEMATICS**

**SECOND TERM** ** **

**WEEK 7**

**PRIMARY 5**

**THEME – MEASUREMENTS AND GEOMETRY **

**PREVIOUS LESSON – Second Term Scheme of Work and Plan Lesson Notes for MATHEMATICS Week 1 to Week 12 Primary Schools**

**TOPIC – AREA OF RIGHT – ANGEL TRIANGLES **

**PERFORMANCE OBJECTIVES **

By the end of the lesson, the pupils should have attained the following objectives (cognitive, affective and psychomotor) and should be able to calculate the area of a right angled triangle.

**ENTRY BEHAVIOUR **

Rectangle

**INSTRUCTIONAL MATERIALS**

The teacher will teach the lesson with the aid of cuboid, rectangle and triangle.

**METHOD OF TEACHING – Choose a suitable and appropriate methods for the lessons.**

*Note – Irrespective of choosing methods of teaching, always introduce an activities that will arouse pupil’s interest or lead them to the lessons. *

**REFERENCE MATERIALS**

1. Scheme of Work

2. 9 – Years Basic Education Curriculum

3. Course Book

4. All Relevant Material

5. Online Information

**CONTENT OF THE LESSON **** **

**LESSON ONE – INTRODUCTION **

Pupil’s Activities 1 – Properties of Cuboid

**Teacher’s Activities – Questions **

1. The objects below is called ______________.

2. What shape does represent in mathematics?

3. How many faces does the objects has?

4. Many corners or vertices does it have?

5. The object is used for ______________.

6. Mention 5 objects that can be packaged inside.

**Note – Guides or leads the pupils where necessary. **

**Pupil’s Response **

1. Carton or box

2. Cuboid

3. Six (6) faces

4. Eight vertices (corners)

5. Packaging

6. Indomie, wine, milk, television, radio, Maclean, chalk, marker, etc.

Teacher’s/Pupil’s Activities 2 – Introduction to Rectangle

**Teacher’s Activities – Cut one of the faces of the carton. Asks pupils to draw and name it. **

**Pupil’s Response – R****ectangle **

Pupil’s Activities 3 – Lengths of Rectangle

**Instructions/Questions **

1. Measure each length of the rectangle.

2. Compare each length with another.

3. Use measurements to describe what rectangle means.

4. Mention 5 objects with rectangular face or shape.

**Pupil’s Response **

1. 10 cm, 7 cm, 10 cm and 7cm.

2. Two of the lengths are equal to each other.

3. Rectangle is a shape with 4 length. Two of its lengths are equal to another.

4. Board, sheet of paper, door, wall or floor, top of desk, etc.

**Teacher’s remark – A rectangle is a 4 sided with opposite parallel lengths are equal length. It is one of the group called quadrilateral. **

**LESSON TWO – RECTANGLE AND TRIANGLE**

Pupil’s Activities 1 – Measure the Lengths of Rectangle

Teacher’s remark – The length and Breadth of rectangle are 7 cm and 3 cm.

Pupil’s Activities 2 – Area of Rectangle

Find the area of rectangle in activities 1 by multiplying length by Breadth.

Area = Length x Breadth

= 7 cm x 3 cm

= 21 cm²

Pupil’s Activities 3 – Cutting Out A Right Angle Triangle

Instructions

1. Draw a diagonal and cut out the rectangle.

2. Then cut along the diagonal.

3. What shape did you cut out.

Teacher’s remark – Two right angles are made up of a rectangle.

Teacher’s/Pupil’s Activities 2 – Area of Triangles

Draw and find the area of a rectangle of length 8 cm and breadth 5 cm.

Area = 5 cm x 8 cm

= 40 cm²

Teacher’s question – If the area of the rectangle is 40 cm², what is the area of triangle if the rectangle is cut through the diagonal?

Expected pupil’s response – The area of triangle is half of the rectangle. That’s, 40 cm² ÷ 2 = 20 cm²

Pupil’s Activities 2 – Class Exercise/Take Home

Draw and find the area of rectangle whose

1. Length 12 cm and breadth 3 cm.

2. Length 15 cm and breadth 6 cm.

3. Length 4 cm and breadth 8 cm.

Then, find the area of triangle if the rectangle is cut through the diagonal.

**LESSON THREE – AREA OF TRIANGLES (½ b x h) **

Teacher’s/Pupil’s Activities 1 – Area of Triangles

Area of rectangle = Length x Breadth

= L x B

Area of Triangle = ½ x L x B

= ½ x B x H or ½bh

Where B stands for the base of the length and H is the breadth.

Pupil’s Activities 2 – Application of ½bh

Find the areas of the triangle below,

Area of Triangle = ½bh,

Where b = 8 cm and h = 6 cm

Therefore,

A = ½ x 8 cm x 6 cm

= 4 cm x 6 cm (8 cm ÷ 2 = 4 cm)

= 24 cm²

Pupil’s Activities 3 – Class Exercise/Take Home

Find the areas of triangles which have these sides,

1. Base is 4 cm and height is 5 cm.

2. Base is 12 m and height is 6 m.

4.

**LESSON FOUR – QUANTITATIVE REASONING **

As stated in the quantitative book or textbook.

**PRESENTATION**

To deliver the lesson, the teacher adopts the following steps:

1. To introduce the lesson, the teacher revises the previous lesson. Based on this, he/she asks the pupils some questions;

2. Guides pupils to divide a rectangle into two halves along its diagonal to form two equal right angled triangles.

3. Guides pupils to derive the formula for area of right angled triangles i.e. 1⁄2 of area of rectangle of 1⁄2 (base × heights).

4. Guides pupils to calculate the area of the right angled triangle.

Pupil’s Activities – Derive and use formula to calculate the area of a right angled triangle.

**CONCLUSION**

To conclude the lesson for the week, the teacher revises the entire lesson and links it to the following week’s lesson.

**LESSON EVALUATION **

**Pupils to ****find the area of a given right angled triangle.**