CBSE Lesson

Geometric Twins: Discovering Congruence

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7th Grade5E Model7.G.B.440 min

Learning Objective

Students will identify congruent figures by matching corresponding sides and angles, state congruence using correct notation, and apply SSS and SAS congruence criteria to determine if two triangles are congruent.

Lesson Overview

Students explore the concept of congruence by investigating when two figures are 'geometric twins' — identical in shape and size. They learn to identify congruent figures, name corresponding parts, and apply congruence criteria for triangles.

Materials

Paper
Pencil
Whiteboard and markers

Scaffolded Task Progression

1Task 1

Look at the two triangles below. Without measuring, write two observations about how they look the same and one way they might look different.

[ Interactive graph / diagram, available in the full lesson ]

[ Interactive graph / diagram, available in the full lesson ]

Do you think these are 'geometric twins'? Write yes or no and one reason.

2Task 2

The teacher has drawn three pairs of triangles on the board with side lengths marked. Copy the table below and fill it in for each pair.

Pair	Triangle 1 sides	Triangle 2 sides
A	3 cm, 4 cm, 5 cm	3 cm, 4 cm, 5 cm
B	3 cm, 5 cm, 6 cm	3 cm, 5 cm, 7 cm
C	4 cm, 4 cm, 4 cm	4 cm, 4 cm, 4 cm

After filling the table, answer: What must be true about the sides for two triangles to be congruent?

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