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SAI International School

CLASS - IX

Mathematics
Chapter7: Triangles

ACTIVITY-1

Sub Topic:Verify the Different Criteria for Congruency of Triangles

OBJECTIVE

To verify experimentally the different criteria for congruency of triangles using triangle cut outs

Materials Required

1. Cardboard
2. Scissors/cutter
3. White paper
4. Geometry box
5. Colored glazed papers
6. Adhesive

Prerequisite Knowledge

1. Concept of congruency of figures.
2. Different criteria for congruency of two triangles.

Theory

1. Congruent Figures Two figures are said to be congruent, if they are of same shape and of same
size (‘congruent’ means equal in all respects).
e.g. Two circles of the same radii and two squares of the same sides are congruent.
Congruency of Triangles -Two triangles are congruent, if sides and angles of a triangle are
equal to the corresponding sides and angles of the other triangle .
Or
If a triangle coincides or covers the other triangle completely, then the two triangles are
congruent.

If ΔPQR is congruent to ΔABC, then we write ΔPQR ≅ ΔABC. Here, ‘≅’ is the sign of congruency.
In congruent triangles, corresponding parts are equal and we write it in short CPCT, i.e.
corresponding parts of congruent triangles.
2. Criterion for Congruency of Two Triangles