Notes on Number System | Grade 7 > Optional Maths > Number System and Surds | KULLABS.COM

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### Number System

Mathematics is the study of numbers and it starts from the number system. According to our level, we shall start from Real numbers. The chart below explains about the number system:

#### Natural numbers ( N )

You can see a number line having a set of numbers are positive. In the figure the possesses will never end if we continue the process.So, marked numbers are called natural numbers which are denoted by N.Here, the natural numbers are 1, 2, 3, 4, 5......

1. The first natural numbers is 1 which is also the least natural number.
2. The next natural numbers can be obtained adding 1 to any natural number.

#### Zero

Before only numbers except zero has been used. Zero usually means the emptiness which is denoted by 0. It is middle numbers between positive and negative numbers.

#### Whole numbers ( W )

A set of the natural number along with zero is called whole numbers which are denoted by W. Hence, whole numbers W = 0, 1, 2, 3, . . . . . .

1. It is the first and the least whole number is 0.
2. It is next whole number which is obtained by adding 1 to any whole number

#### Integers ( $$\mathbb{Z}$$)

We know ,
Natural numbers are = 1, 2, 3, 4, 5, ....... and Negative natural numbers are = -1, -2, -3, -4, -5, ......

Therefore, the set of all positive natural numbers, negative natural numbers inclusive of zero is known as integers. It is denoted by $$\mathbb{Z}$$.

So, $$\mathbb{Z}$$ = ........, - 3, - 2, - 1, 0, 1, 2, 3, .......

figure

Note :

1. Positive integers : ( $$\mathbb{Z}$$+ )
The set of all natural numbers is known as positive integers.It is denoted by $$\mathbb{Z}$$+ .
∴ Z= 1, 2, 3, 4, ............ = N.
2. Negative Integers: ( $$\mathbb{Z}$$):
The set of all negative natural numbers is known as integers.It is denoted by $$\mathbb{Z}$$
∴ Z= - 1, - 2, - 3, .........
3. O ( Zero ) is neither positive integers nor negative integer .It is a natural number.

#### Rational Number (Q)

A number that can be written in the form of $$\frac{p}{q}$$ where q ≠ o is called rational number .It is derived from the word ratio which also satisfies the structure $$\frac{p}{q}\}. Note:p and q also needs to be integers eg: \(\frac{2}{3}$$ , $$\frac{5}{9}$$, 0 etc .

Properties of rational numbers

1. Here, decimals of rational members are either terminating or recurring .Any rational number can be written in a ratio .Hence, it was divided .When they are divided the decimals are either terminating or repeating.
Eg: $$\frac{1}{2}$$
$$\require{enclose}\begin{array}{r}0.5\\[-3pt]2\enclose{longdiv} {10}\\[-3pt]\underline{−10} \end{array}$$
Divident = 1
Divisor = 2
Here, $$\frac{1}{2}$$ = 0.5 which is terminating decimal.

#### Irrational Numbers ($$\overline{Q}$$ )

Those members which can not be expressed in the form of $$\frac{a}{b} \} where a and b both are integers and b ≠ 0 , are called irrational numbers . eg : \(\sqrt{5}$$, $$\sqrt{3}$$, 5$$\sqrt{7}$$, $$\sqrt{3}$$+2, $$\frac{1}{2 + \sqrt{5}}$$,π, 0.303003000 . . . . .
The decimals of irrational numbers are neither terminating nor repeating.

• Nomenclature of an Irrational Number

eg: In $$\sqrt{2}$$ the order of $$\sqrt{2}$$ is 2.
In $$\sqrt[3]{29}$$ the order of $$\sqrt[3]{29}$$ is 3.

• Positive and negative integers are denoted by ( Z+ ) and ( Z- )  respectively.
• 0 ( Zero ) is neither positive integers nor negative integers .It is  a natural number.
• Here, decimals of rational  members  either terminating or recurring .
.

#### Click on the questions below to reveal the answers

Solution

$$\frac{2}{5}$$

= $$\require{enclose}\begin{array}{r}0.4\\[-3pt]5\enclose{longdiv} {20}\\[-3pt]\underline{20} \end{array}$$

Here, Divident = 2

Divisor = 5

Solution

$$\frac{1}{2}$$

= $$\require{enclose}\begin{array}{r}0.5\\[-3pt]2\enclose{longdiv} {10}\\[-3pt]\underline{10} \end{array}$$

Divident = 1

Divisor = 2

Here, $$\frac{1}{2}$$= 0.5 which is terminating decimal.

Solution

=$$\frac{1}{4}$$

=$$\require{enclose}\begin{array}{r}0.25\\[-3pt]4\enclose{longdiv}{10}\\[-3pt]\underline{8}\\[-3pt]{20}\\\underline{20}\end{array}$$

Divident = 1

Divisor= 4

Here, $$\frac{1}{4}$$ = 0.25 which is terminating decimal.

Solution

$$\frac{1}{4}$$

= $$\require{enclose}\begin{array}{r}0.25\\[-3pt]4\enclose{longdiv} {10}\\[-3pt]\underline{8} \\[-3pt]20\\\underline{20}\end{array}$$

=  Here, the quotient is 0.25. It is terminating after 2 decimals.

Divident= 1

Divisor = 4

The properties of rational numbers are listed below:

• Any rational numbers can be written in a ratio.
• It must be divided.
• The decimals of rational members are either terminating or recurring.

0%
• ### If the root of rational number is irrational then the resulting number is called .....................................

Integers
Surds
Whole number
Rational number

0.25
0.24
0.29
0.27

1.41818
1.31818
1.2345
1.32456

0.1332
0.201
0.2113
0.222

0.29
0.25
0.15
0.5

integers
ratio
surds
real numbers
• ### What is this?√5

Irrational number
rational number
natural number
surds
• ### The  set of  all integers is denoted by.......................

(frac{p}{q})
Z
none of the above.
1
• ### 1, 2, 3, 4, 5, 6, ........ are the set  of __________________________ numbers.

Irrational numbers
Whole numbers
natural numbers
rational numbers

0.150
0.275
0.125
0.115

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