Horizontal and Vertical Line Graphs
Key Questions

A horizontal has the equation
#y=b# with#b# any constant number
A vertical has the equation#x=c# with#c# any constant numberA normal linear equation is mostly of the form
#y=mx+b#
where#m# is the slope. In a horizontal graph, the slope is 0.
The#b# (called the#y# intercept) tells you where the graph crosses the#y# axis.For the vertical graph a similar story goes and
#c# is called the#x# intercept. 
Answer:
#x=0# Explanation:
For any point on the Yaxis,
#x# is equal to zero;
furthermore, if any point for which the#x# coordinate is equal to zero will be on the Yaxis. 
The xaxis is like a number line, isn't it? Every point on the xaxis has a ycoordinate of 0 like this: (4,0), (3,0), (2.7, 0) and (0,0).
If all of these points have the same ycoordinate, it follows that the equation of that line must be y = 0! It would be the same idea for any horizontal line, since the slope = 0. Calculate the slope between any two of those points:
m =#(00)/(3(4))# using (4,0) and (3,0).
You would write the equation now like: y = 0x + 0, or just y = 0.Think about another horizontal line that goes through the points (8,3), (0,3), (14, 3), and (4.1, 3). Calculate the slope:
m =
#(33)/(140)# using the points (0,3) and (14,3).
The yintercept is (0,3) and therefore the equation of that line is y = 0x + 3, or just y = 3. 
An equation of a vertical line can be written in the form
#x=a# ,where
#a# is a constant.An equation of a horizontal line can be written in the form
#y=b# ,where
#b# is a constant.
I hope that this was helpful.
Questions
Graphs of Linear Equations and Functions

Graphs in the Coordinate Plane

Graphs of Linear Equations

Horizontal and Vertical Line Graphs

Applications of Linear Graphs

Intercepts by Substitution

Intercepts and the CoverUp Method

Slope

Rates of Change

SlopeIntercept Form

Graphs Using SlopeIntercept Form

Direct Variation

Applications Using Direct Variation

Function Notation and Linear Functions

Graphs of Linear Functions

Problem Solving with Linear Graphs