# Equation Of A Line Parallel To The X-Axis Or Y-Axis

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In this lesson, we will learn

• what is the equation of a horizontal line or a line parallel to the x-axis.
• how to graph the horizontal line using a T-table.
• what is the equation of a vertical line or a line parallel to the y-axis.
• how to graph the vertical line using a T-table.

### Equation of Line Parallel to the x-axis

A line that is parallel to the x-axis and has a y-intercept of c. has the equation y = c. The line is a horizontal line with a slope of 0.

How to graph a horizontal line by using a table of values (T-table)?
Example:
Graph a line using a table of values.
y = -4

### Equation of Line Parallel to the y-axis

A line that is parallel to the y-axis and has a x-intercept of a has the equation of x = a. The line is a vertical line that has no slope and no y-intercept. The slope is also said to be undefined.

How to graph a vertical line by using a table of values?
Example:
Graph a line using a table of values
x = 3

How to graph horizontal and vertical lines?
Example 1:
a) Graph y = -2.
b) The graph consists of all ordered pairs whose y-coordinate is -2.

Example 2:
a) Graph x = 3.
b) The graph consists of all ordered pairs whose x-coordinate is 3.

The graph of y = c or f(x) = c, a horizontal line, is the graph of a function. Such a function is referred to as a t function.
The graph of x = a, a vertical line is not the graph of a function.

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