Page 46 - Mathematics Class - IX

PROCEDURE
1. Take a cardboard of a suitable size and paste a white paper on it.

2. Cut out a pair of ∆ABC and ∆DEF from a glazed paper such that AB = DE, BC = EF and AC = DF (Fig. (a)).

A D

B C E F
Fig. (a)

Superimpose ∆ABC on ∆DEF completely only under the correspondence A ↔ D, B ↔ E and C ↔ F. See
that ∆ABC covers ∆DEF completely.

Hence, ∆ABC ≅ ∆DEF if AB = DE, BC = EF and AC = DF.

This is SSS criterion for congruency.

3. Make a pair of ∆GHI and ∆JKL from a glazed paper such that GH = JK, GI = JL and ∠G = ∠J and cut
them out (Fig. (b)).

G J

H I K L

Fig. (b)

Similarly, superimpose ∆GHI on ∆JKL completely only under the correspondence G ↔ J, H ↔ K and
I ↔ L. See that ∆GHI covers ∆JKL completely.

Hence, ∆GHI ≅ ∆JKL if GH = JK, ∠G = ∠J and GI = JL.
This is SAS criterion for congruency.

4. Make a pair of ∆PQR and ∆STU from a glazed paper such that QR = TU, ∠Q = ∠T and ∠R = ∠U and
cut them out (Fig. (c)).

P S

Q R T U

Fig. (c)
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