Page 24 - Mathematics Class - IX

ACTIVITY 2.3

OBJECTIVE

To verify the algebraic identity: (a – b) = a – 3a b + 3ab – b 3
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2
3
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MATERIALS REQUIRED
Set of unit cubes of (1 cm × 1 cm × 1 cm)

PRE-REQUISITE KNOWLEDGE
1. Volume of cube = (edge) 2. Volume of cuboid = l × b × h
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THEORY
For the concepts of cube and cuboid refer to Activity 2.2

PROCEDURE
1. Take unit cubes and make a cube of (a – b) = 5 units as shown is Fig. (a).

Fig. (a)

2. Let a be 6 and b be 1 unit. Make three cuboids of dimensions 5 × 6 × 1 and one cube of side 1 unit as shown
in Fig. (b).

b b

a a

b
b
a
b
b
Fig. (b)

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