Horizontal Line: Definition, Formula, Properties and Examples

What is a Horizontal Line?

In Cartesian coordinate system, we draw a vertical and a horizontal line.

(1) Y-axis is Vertical and

(2) X-axis is horizontal lines on a plane.

In coordinate system, meaning of horizon is a straight line that is mapped from left to right.

A horizontal line is a straight line that goes from left to right or right to left.

It means that the horizontal lines are always parallel to the the same Y-coordinate points.

X axis is called the horizontal line. Horizonal lines are parallel to X axis.

In other words, a line is said have to be horizontal if two points on the line that does not make any intercept on the X-axis and it can have an intercept on Y-axis is called horizontal line.

This means that the Horizontal lines are parallel to x-axis and does not touch any point on the X axis.

Equation of Horizontal Line

We can define a horizontal line in the form of an equation. The equation of horizontal line is represented as y = b

where b is any value(constant) on the y-axis.

It is observed that the horizontal lines have the same slope, so the slope of the horizontal line is always zero.


A horizontal line is a line on the coordinate plane, where all points on the plane have the same Y-coordinate.

Any point in this line will have same value for the y-coordinate.

Example: (0, 3), (0, 5) (0, -4) etc. are the points of horizontal lines.

We can understand this by the horizontal lines mapped on a coordinate plane.

Plot the graph for the (i) y = 3 and (ii) y = -4.

When we plot a point on a plane surface, we take two axes.

(1) X-axis (2) Y-axis

(i) y = 3

y = 3 is a horizontal line, that passes through y-axis, at a distance of 3 units on the above of the origin and is parallel to x-axis.

(ii) y = -4 is a horizontal line, that passes through x-axis, at a distance of 4 units on the below of the origin and is parallel to x-axis.

Properties of horizontal lines

(i) In a coordinate plane, horizontal line is parallel to x-axis.

(ii) A vertical line is always perpendicular to the horizontal line.

(iii) The slope of a horizontal line is always zero.

(iv) Horizontal line is parallel to horizon.

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