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Home
Maths
Horizontal Line

Horizontal Line 

A line is a straight figure that extends infinitely in all directions without curvatures; it has no width or thickness but length. A horizontal line refers to a special type of line running from left to right, parallel to the horizon.

Horizontal and Vertical line

1.0A Brief Overview of Horizontal Line 

A horizontal line runs parallel to the horizon and is perpendicular to any vertical line. A horizontal line refers to a line that has a slope equal to zero. Thus, this line is neither sloping nor declining, a completely flat line from the origin of its length. This, in turn, disqualifies it from many kinds of lines like the case with a vertical or slanting line.

2.0Key Characteristics of a Horizontal Line

  1. Slope: Slope is the steepness or incline of a given line. It is the vertical change (rise) with respect to the horizontal distance (run). Hence, The slope of a horizontal line is always 0, since the rise is 0 for any change in run. On the other hand, the slope of a vertical line is undefined. The slope of a line for given coordinates says (x1, x2) and (y1,y2) is: 

Slope(m)=RunRise​=x2​−x1​y2​−y1​​

  1. Horizontal line equation: The general equation for any line with coordinates (x,y) and slope m can be given as: 

y=mx+c

Since the slope for a horizontal line is 0, therefore 

y=c

where c is the constant, the y-coordinate of any point on the line. In other words, points along a horizontal line all have the same y-coordinates while their x-coordinates are all different. It is known as the horizontal line equation.

Horizontal line equation

3.0Horizontal Line and Vertical Line

A horizontal line and a vertical line are always perpendicular to each other and form a 90-degree angle at their intersection. The horizontal line has a slope of 0, while the vertical line has an undefined slope. The relationship is important in geometry, used to define coordinates and graphing functions, and divides a plane into different regions.

Horizontal line and Vertical line

4.0Difference Between Horizontal Line And Vertical Line

Horizontal Line

Vertical line

A horizontal line runs from left to right or right to left in a plane. 

The Vertical line runs from up to down or down to up in a plane.

It is parallel to the x-coordinate of the plane. 

It is parallel to the y-coordinate of the plane. 

The slope of a horizontal line is always 0.

The slope of the vertical line is not defined. 

It doesn’t intersect the y-axis. 

The vertical line doesn’t intersect the x-axis. 

The equation of a horizontal line is of the form y = c, where c is a constant.

The equation of a vertical line is of the form x = c, where c is a constant.

5.0Horizontal Line Test

A method for determining whether a function is one-to-one is by horizontal line test. If a horizontal line intersects the graph of the function at more than one place, then the function fails to pass the test. This will guarantee that there exists exactly one x-value for each y-value; thus, the function is invertible. If a horizontal line crosses the graph at more than one place, the function fails the test and is not one-to-one; thus, it doesn't have an inverse. This Horizontal Line test is a way to assess the behaviour of functions.

Horizontal Line Test

6.0Drawing A Horizontal Line

For drawing a horizontal line, start at any point on a grid or surface. Then, draw a straight line from left to right, keeping it level and not tilting up or down. This line must run parallel to the x-axis, with the same y-coordinate along its length. Let us understand in more detail how to draw horizontal lines with the help of some examples of horizontal lines.


Example 1: Draw a horizontal line that represents the bottom edge of Sarah’s garden, which is at a height of 2 feet above the ground. Label the line with its equation.

Sample Question on Horizontal Line

Solution: y = 2


Problem 2: Draw the horizontal line representing the x-axis, which passes through the origin (0, 0). Label the line with its equation.

Solution: Let the coordinate for the horizontal line be (0,4) 

The Equation will be y = 4. 

Practice Question on Horizontal Line

Problem 3: Draw a horizontal line at a height of -3 on a graph. Label the line with its equation.

Solution: y = –3 

Sample Question on horizontal line

7.0Also Read

Standard Units of Measurement

Circles

Introduction to Numbers

Ascending Order

Area of Rectangle

Roman Numerals

Area of Irregular Shapes

Laws of Exponents

Rounding Numbers

Table of Contents


  • 1.0A Brief Overview of Horizontal Line 
  • 2.0Key Characteristics of a Horizontal Line
  • 3.0Horizontal Line and Vertical Line
  • 4.0Difference Between Horizontal Line And Vertical Line
  • 5.0Horizontal Line Test
  • 6.0Drawing A Horizontal Line
  • 7.0Also Read

Frequently Asked Questions

A horizontal line example remains at the same y-coordinate throughout the entire graph. For instance, the equation y = 3 is a horizontal line at a constant height of 3.

The horizontal line test tells whether or not a function is one-to-one. If any horizontal line intersects the graph at more than one place, the function fails the test and is not one-to-one.

No, a horizontal line always has a slope of 0. A negative slope would mean that the line slopes downward, which contradicts the definition of a horizontal line, which does not slope at all.

Horizontal lines are basic in geometry for defining shapes, graphing functions, and helping with concepts like symmetry, coordinate systems, and slope, especially in determining relationships between different variables.

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