Horizontal and Vertical Lines
Horizontal lines are parallel to the x-axis.
A line parallel to the x-axis that passes through the y-intercept, b, is expressed by the equation: y = b
Vertical lines are parallel to the y-axis.
A line parallel to the y-axis that passes through the x-intercept, a, is expressed by the equation: x = a
The equation of the x-axis is y = 0.
The equation of the y-axis is x = 0.