Natural Numbers, Whole Numbers and Integers - Number Systems, Class 9, Mathematics PDF Download

INTRODUCTION
"God gave us the natural numbers, all else is the work of man". It was exclaimed by L. Kronecker (1823-1891), the reputed German Mathematician. This statement reveals in a nut shell, the significant role of the universe of numbers played in the evolution of human thought.
N: The set of natural numbers,
W: The set of whole numbers,
Z: The set of Integers,
Q: The set of rationals,
R: The set of Real Numbers.
In our day to day life, we deal with different types of numbers which can be broadly classified as follows.

1. Natural Numbers (N): The counting numbers 1, 2, 3, ..... are known as natural numbers. The collection of natural number is denoted by 'N'.
N = {1, 2, 3, 4...∞}

2. Whole numbers (W): The number '0' together with the natural numbers 1, 2, 3, .... are known as whole numbers. The collection of the whole numbers is denoted by 'W'.
W = {0, 1, 2, 3, 4...∞}

3. Integers (I or Z): All natural numbers, 0 and negative of natural numbers are called integers. The collection of integers is denoted by Z or I. Integers (I or Z) : I or Z = {–∞, ..... –3, –2, –1, 0, +1, +2, +3 .... +∞}. Positive integers : {1, 2, 3...}, Negative integers : {.... –4, –3, –2, –1}.