X and Y are the names given to the vertical and horizontal planes in 2 dimensional geometry, respectively. Therefore any number (2 or 7 or 4 or 5.76889) that x equals will run vertically as x is based on the vertical axis. However, the number line for X runs horizontaly; thus creating all numbers that x equals as a vertical line.

In the equation x=4, there is no meaningful variable. X will always equal 4, so at any point on the Y-axis, the X co-ordinate must be 4. This causes the graph to be a verticle line passing through the x-axis at 4.

Worthy of note, it is not a funtion, because in a function, no number in the domain can equal more than one number in the range. X=4 produces infinite Y co-ordinates with only one value in the domain, and thusly does not qua...

In the equation x=4, there is no meaningful variable. X will always equal 4, so at any point on the Y-axis, the X co-ordinate must be 4. This causes the graph to be a verticle line passing through the x-axis at 4.

Worthy of note, it is not a funtion, because in a function, no number in the domain can equal more than one number in the range. X=4 produces infinite Y co-ordinates with only one value in the domain, and thusly does not qualify.