Horizontal line

Definition

A horizontal line is a straight line that runs left to right and has a constant y-value for all points on the line. In a Cartesian coordinate system, its slope is zero.

5 Must Know Facts For Your Next Test

1. The equation of a horizontal line can be written as $y = c$ where $c$ is a constant.
2. A horizontal line has a slope of zero because there is no vertical change between any two points on the line.
3. In the context of linear functions, a horizontal line represents a function where the output value remains constant regardless of the input value.
4. Horizontal lines are parallel to the x-axis in the Cartesian plane.
5. If two lines are both horizontal, they are either identical or parallel.

Review Questions

• What is the slope of any horizontal line?
• How do you write the equation of a horizontal line passing through (2, 3)?
• Are all horizontal lines parallel to each other?

Related terms

Vertical Line: A vertical line runs up and down with an undefined slope and can be described by an equation in the form $x = k$ where $k$ is a constant.

Slope: $m$, defined as $\frac{\Delta y}{\Delta x}$, measures the steepness or incline of a line in relation to the x-axis.

$y$-intercept: $b$, represents the point where a line crosses the y-axis.