# Maths formulas for class 9 chapter- Number System Formula

## Class 9 chapter- Number System Formula

• Natural Numbers: Counting numbers started by 1 are called “Natural numbers”. The set of natural numbers is denoted as N = {1, 2, 3, ∞}.
• Whole Numbers: Natural numbers including “0” (zero) are called whole numbers. The set of whole numbers is W = {0, 1, 2, 3, ……}.
• Integers: Whole numbers including natural numbers with negative sign are called “Integers”.

The set of integers is I or Z = {……, -3, -2, -1, 0, 1, 2, 3, ……}

1. Odd numbers- 1, 3, 5, 7, ……
2. Even numbers- 0, 2, 4, 6, ……
3. Prime number- Number divisible by one and itself only 2, 3, 5, 7, 11, 13, 17, ……
• Rational Numbers: Number of the form p/q where p,q, ∈and q ≠ 0 are called rational numbers.

Q = {p/q,p & q are integers & q≠0}

### Decimal form of rational numbers

• The number of digits are finite after decimal (Terminating decimal). For example- (a) –0.5  (b) 3.654
• The number of digits are infinite after decimal and repetition of the digits are then (non-terminating, recuring decimal).

For exmaple-

• Irrational numbers- Numbers which are non-terminating, non-recurring are called irrational numbers. Example:√2,√3,√7.

The most popular irrational number

1. Π = 3.1459265 ……
2. e = 2.7182818

Some results on irrational numbers:

1. Negative of an irrational number is an irrational number.
2. SUM, DIFFERENCE, PRODUCT & QUOTIENT of rational and an irrational number is an irrational number.
3. SUM, DIFFERENCE, PRODUCT & QUOTIENT of two irrational numbers may be rational or an irrational number.
• Real numbers- Numbers including rational and irrational numbers are called “real numbers”.

1. Each and every point on the line represents a definite real number.
2. Each and every real number has definite chair on number line.
3. All real numbers can be represented on a number line.

NCERT Solutions are very helpful to score good marks in Class 9 Maths do solve questions from text book with the help of NCERT Solutions for class 9 Maths prepared by academic team of Physics Wallah. Download the pdf of maths formulas for class 9 chapter- Number System from Physics Wallah.

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