# Subject : Mathematics

## 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

1. A right angled triangle : This is a triangle that has one of its interior angles equal to 90 degrees
2. An equilateral triangle :  This is a triangle that has all the three angles and sides equal
3. A Scalene triangle : This type of triangle has no equal sides
4. 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 :