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How to plot a horizontal or vertical line like x = 4 or y = -2

Updated on April 4, 2011

A horizontal line (-) has the formula:

y = a number

A vertical line (|) has the formula:

x = a number

Question 1

Plot the line x = 4.

Basically, this is a vertical line which passes through the number x = 4 on the x axis.

Notice that the line is perpendicular (at a right angle) to the x axis, and not parallel to the x-axis. Also, any point that is on the line has an x coordinate of 4.

Question 2

Plot the line y = -2.

This time you have a horizontal line as the formula is y = a number. Therefore, the line passes through the y axis at y = -2.

Notice again, that the line is perpendicular to the y axis and not parallel to it. Also, if you pick any point on the line then the y coordinate will be -2.

Question 3

Plot the lines x= 2.5 and y = -3.

Also write down the point of where the two lines intersect.

x = 2.5 is a vertical line that passes through the x axis at 2.5 (a vertical line)

y = -3 is a horizontal line that passes through the y axis at -3 (a horizontal line)

Now, the intersection point of the two graphs is where the two lines cross.

Therefore, the intersection point of our two lines is (2.5,-3). Notice they are the numbers that are in both formulas.

For some more hubs on graphs check these out:

How to draw a quadratic graph (a curve or parabola). Like y=x^2 -2x -5

Straight line graphs. How to plot a sloping line in math using a table of values.


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  • Didge profile image

    Didge 5 years ago from Southern England

    awesome! So creative :)