Page 14 - Mathematics Class - IX

ACTIVITY 1.2

OBJECTIVE
To represent some irrational numbers on the number line.

MATERIALS REQUIRED

Squares of unit length Coloured papers of two different colours
Geometry box
PRE-REQUISITE KNOWLEDGE

1. Concept of number line 2. Concept of Pythagoras theorem

THEORY
For all concepts, refer to Activity 1.1.

PROCEDURE
1. Draw a straight line X´OX as shown in Fig. (a) and mark the unit length as 1, 2, 3... and – 1, – 2,
– 3,... on either side of origin.
O
X´ X
–3 –2 –1 0 1 2 3
Fig. (a)
2. Cut the square blocks from different coloured papers of same unit length as marked on the number line, as
shown in Fig. (b).
B

O A
Fig. (b)
3. Fold the square block along the diagonal and place it on the number line as shown in Fig. (c).
B

O A
X' X
–3 –2 –1 0 1 2 3
Fig. (c)
4. The length of the diagonal OB represents 2 as ∆OAB is a right-angled triangle.

So, OB = OA + AB 2
2
2
⇒ OB = 1 + 1 2
2
2
⇒ OB = 2
12