Session 37: Triangles

Introduction Activity (15 minutes): 

Mandala Patterns 

• Concepts: Circles, radial symmetry, angles, pattern repetition

How:

• Students use compasses and protractors to make mandalas.
• Emphasizes symmetry and repeated geometric patterns.
• Can be colored for relaxing mindfulness activity too.

Example: (Draw the picture given below on a chart)

Main Activity (65 minutes):

What’s a Triangle?  Discussion (10 minutes):

• Show pictures of different shapes (triangle, square, rectangle, circle).
• Ask: Which one is a triangle? How do you know?
• Students share prior knowledge.
• Teacher highlights: A triangle has 3 sides and 3 angles. It’s a closed shape.

Story Time (15 minutes):

In the Triangle Kingdom, every triangle has a secret code: its 3 angles must always work together to form a straight line (180°) to keep the kingdom safe!

Characters:-

•  Prince Equi (Equilateral)
•  Sir Righty (Right triangle)
•  Lady Acuta (Acute triangle)
•  General Obtusa (Obtuse triangle)

The sum of the interior angles of any triangle is always equal to 180 degrees.

In mathematical notation, for a triangle ABC with interior angles angle A, angle B, and angle C, the triangle sum theorem can be expressed as:

‹A + ‹ B + ‹C = 180⁰

Ask: Can you guess how their angles work together?  

Student Engagement (10 minutes):

Ask students to act out triangle characters (e.g., stretch arms to represent different angles).

Key Concept (10 minutes):

Definition of a triangle

• A closed figure with 3 sides and 3 angles.

Types of triangles by sides

• Equilateral (3 equal sides)
• Isosceles (2 equal sides)
• Scalene (no equal sides)

Types of triangles by angles

• Acute triangle (all angles < 90°)
• Right triangle (one angle = 90°)
• Obtuse triangle (one angle > 90°)

Group Activity- Angle Detectives (20 minutes):

Make students into small groups(3 or 4)

• Give each group a work sheet of  triangle with one missing angle.
• Students solve for the missing angle by subtracting from 180°.

Review Questions (5 minutes):

1. What is a triangle?
2. How many angles does a triangle have?

Follow up Task (5 minutes):

1. Name a real-life object or structure that uses a triangle shape. Why is it used?
2. Draw a triangle where one angle is 90°. What type of triangle is it?

Expected Learning Outcome:

Knowledge building:

• This focuses on conceptual understanding and facts. You help students understand what a triangle is, its types, and properties.

Skill building:

• Conceptual understanding
• Problem solving

Resources:

Missing triangles