A coordinate system that expresses the exact position of a point on a straight horizontal line is defined as number line.

Number line

Number line is a basic coordinate system in geometric mathematics. It is used to identify the exact position of a point on a line which is divided into numerous equal parts. Each part represents a unit length and the centre of the number line is known as its origin.

Real numbers system is used to represent every unit and the origin is considered as position of zero. Positive real numbers denote the each part in right side of the number line from the origin. Negative real numbers denote the each part in left side of the number line from the origin.

A number line can be constructed in four simple steps.

- Draw a straight line on a plane.
- Identify the exact middle point of the straight line and it is called origin of the number line. Denote it by zero ($0$).
- Denote each part of the right side origin by positive real numbers $1,2,3,\dots \infty $
- Similarly, denote each part of the left side origin by negative real numbers $\u20131,\u20132,\u20133,\dots \u2013\infty $

A person started from his home, walks on the surface of the earth and reached his office. We don’t know exactly where he is and also don’t how much distance he traveled from his home to reach his office.

Without an appropriate system, we cannot tell exactly where he is and distance he travelled. Number line coordinate system is a really useful coordinate system which helps us to find a solution for such issues.

Consider the number line coordinate system and assume it is in kilometers. Assume, the location of his home is zero and the location of his office is at $2$.

The distance from his home to office is $2$ kilometres because there are two equal parts between the person and home in the number line. Therefore, his office is $2$ kilometres away from his home and the distance he travelled from his home to office is $2$ kilometers.

Number line coordinate system helped us to know the exact location of the person. In this way, it is mainly used to know the position of anything in a straight line path.

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