## ICSE Class 9 Maths Chapter 1 Rational and Irrational Numbers Revision Notes

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## Natural numbers

The positive integers are called natural numbers.

#### Types on natural number:

**Even Natural Numbers:** If it is a multiple of two then it is called even natural number. … A value of the form 2n, where n is a counting number. e.g. 2, 4, 6, 8, 38…..

**Odd Natural Numbers:** An odd number is one which is not divisible by 2 and the first odd natural number is 1. e.g. 1, 3, 5, 7, 9…

**Prime Numbers:** These are the numbers that are exactly divisible by only 1 and the

number itself. e.g., 1, 3, 5, 7, 11, 13…

## Rational Numbers

Any number which can be put in the form of p/q where p and q are integers and q is not equal to zero, is called a rational number. There exist an infinite number of rational numbers between any two rational numbers.

For example, between 7 and 7.5 there exist 7.1, 7.11, 7.21, etc.

## Irrational Numbers

Those numbers which cannot be expressed in the form of p/q where p, q are integers, and q not equal to zero are called irrational numbers.

The sum, difference, product, or quotient of two irrational numbers may not be an

irrational number. The negative of an irrational number is also an irrational number.

Examples are 1.8632457…, √2, etc.

### ICSE Class 9 Maths Chapter 1 Rational and Irrational Number Revision Notes PDF