Chapter 3 ยท CBSE Class 9 Maths (NCERT Ganita Manjari Part 1)

The World of Numbers

Explore the real number system, including rational and irrational numbers, and their representation on the number line.

๐Ÿ”ข Chapter 3

3.1

The Real Number System

Real numbers include all rational numbers (expressible as p/q) and irrational numbers (non-terminating, non-repeating decimals like โˆš2 and ฯ€).

1

Is 0.333... (repeating) rational or irrational?

Rational, since it equals 1/3, expressible as p/q

2

Is โˆš5 rational or irrational?

Irrational, since 5 is not a perfect square

3.2

Representing Numbers on the Number Line

Both rational and irrational numbers can be represented precisely on the number line, with irrational numbers like โˆš2 located using geometric construction.

1

How can โˆš2 be located on the number line using a right triangle?

Construct a right triangle with legs 1 and 1; the hypotenuse has length โˆš2, which can be transferred to the number line using a compass

2

Between which two integers does โˆš10 lie?

3 and 4, since 3ยฒ=9<10<16=4ยฒ

Practice

Exercises

1. Is 0.25 rational or irrational?

2. Is โˆš11 rational or irrational?

3. Between which two integers does โˆš20 lie?

4. Is 22/7 rational or irrational?

5. Simplify: โˆš18