# Types of Triangles

**Subject** : **Mathematics**

**Mathematics**

**Class** : Basic 6 / Primary 6 /Grade 6

**Term** : Third Term / 3rd Term

**Week** : Week 5

**Topic** : Types of Triangles

**Behavioural Objectives :** At the end of the lesson, the pupils should be able to

**Explain the meaning of triangles**- Give examples of triangles
- Mention types of triangles
- Say the properties of triangles

**Previous Knowledge : Pupils have previous knowledge of Polygons and plane figure that was taught in the previous lesson**

**Instructional Materials** :

- Pictures
- Wall Posters
- Related Online Videos
- Role Playing

**Reference Materials**

- Scheme of Work
- Online Information
- Textbooks
- Workbooks
- 9 Year Basic Education Curriculum

**Content** :

** Types of Triangles**

Triangles are three sided shapes . They have three sides and three angles . The angles in the triangles are called interior angles while the angles that are outside are called exterior angles . A triangle can also be formed by using a diagonal line to divide a square or a rectangle diagonally . . These are the types of triangles that we have

- A right angled triangle : This is a triangle that has one of its interior angles equal to 90 degrees
- An equilateral triangle : This is a triangle that has all the three angles and sides equal
- A Scalene triangle : This type of triangle has no equal sides
- An Isosceles triangle : This is a triangle that has two equal sides or angles

The area of a triangle is obtained when the value of half of the base is multiplied by the height

Area = ** ^{1} / _{2}** ×

**base**×

**height**.

The line that is directly opposite the right angle is called the Hypotenuse .

Mental Sums on Types of Triangles

1. What is a triangle

2. Define scalene triangle

3. Triangles are three sides shapes . True or false

4. What is an equilateral triangle

5. A plane shape that has three sides and angles is called a ________________

6. The value of the right angle in a triangle is equal to _______________________

7. The angle of a triangle is in the ratio of 2: 3: 4. Find the measure of each angle of the triangle.

8. One of the two equal angles of an isosceles triangle measures 55°. Determine the other angles.

9. The perimeter of a triangle is 24 cm. Two of its sides are 8 cm and 9 cm. Find the length of its third side.

10. Each side of a ∆ is one third of its perimeter. What kind of triangle is this?

11. One of the acute angles of a right triangle is 48°. Find the other acute angle.

12. Say whether the following statements are true or false:

(a) All the angles of an isosceles triangle are equal.

(b) If one angle of a triangle is obtuse, the other two angles must be acute.

(c) A right triangle can be equilateral.

(d) Quadrangular triangle has its three sides also equal.

(e) A triangle can have two obtuse angles.

**Presentation**

The topic is presented step by step

Step 1:

The class teacher revises the previous topics

Step 2.

He introduces the new topic

Step 3:

The class teacher allows the pupils to give their own examples and he corrects them when the needs arise

**Evaluation** :

**Assignment** :

Prepare for the next lesson by reading about

Types of Angles and Shapes