This document discusses classifying triangles based on side lengths and angle measurements. Triangles can be equilateral, isosceles, or scalene based on equal or unequal side lengths. They can also be acute, obtuse, right, or equiangular based on angle measurements. The document defines each type of triangle and provides examples. It discusses determining congruency or similarity of triangles based on side lengths and angle criteria. The objectives are to recognize different triangle types and properties and determine congruent or similar triangles.

1. Classifying triangles
Similarity and congruency

2. Introduction
Do you still remember what is a triangle?
A triangle is a polygon with three sides and three angles.
side
angle

3. We can classify a triangle in 2 ways
By the length of the sides
Equilateral
Isosceles
Scalene
By the measurement of the
angles
• Acute
• Obtuse
• Right-angle
• Equiangular

4. Objectives
At the end of the lesson, learners must be able to:
Recognize different types of triangles and their properties.
Determine congruent triangles.
Determine similar triangles.

5. Classification according to
Sides

6. Equilateral triangle
All sides are equal in length.

7. Isosceles triangle
• Two sides are equal in length
𝐴𝐵 = 𝐴𝐶

8. Scalene triangle
• All sides have different lengths

9. Classification according to
Angles

10. Acute triangle
• All angles are acute (less than 90˚)

11. Obtuse triangle
• One angle is obtuse (more than 90˚)
Obtuse angle

12. Right-angled triangle
• One angle is right-angled (equal to 90˚)

13. Equiangular triangle
• All angles are equal (60˚)

14. Angles of a triangle
• The sum of interior angles of a triangle add up to 180˚

15. What is the size of the missing angle?
𝐶 = 180˚ − 38˚ − 85˚ = 57˚

16. Exercise: Classify these triangles.
A B
Right-angled triangle Scalene

17. Exercise: Classify these triangles.
conti
Isosceles Obtuse triangle
C D

18. Conditions for congruency and similarity
Congruency
SSS
SAS
ASA
RHS
Similarity
AAA
SSS
SAS

19. Determining congruency

20. Determining Similarity

21. To check if you understand:
Access the link below for an activity on congruency and
similarity:
http://goo.gl/thJNqR