Vertical line test

A vertical line test is a visual way to determine if the graph of a relation is a function.
If the vertical line passes through at least two points on the graph, then 1 element in the domain is paired with more than 1 element in the range. 

The line has to be vertical. Below see a correct vertical line test and an incorrect vertical line test.

Next, we show you a few examples where the vertical line test was used to determine if the graph is a function. 

Example #1

Not a functionVertical line test

Notice the two blue points. This means that the vertical line passes through 2 points. 
Can you guess what these two points are just by looking at the graph?

These two points are (4, 1) and (4, 3). As you can see, 4 is paired with two elements and again that is why it is not a function.

Example #2

Is a functionVertical line test

Here, there are 5 vertical lines and none of them passes through at least 2 points. Therefore, this graph is a function.

Feel free to draw as many vertical lines as possible before you draw your conclusion.







Recent Articles

  1. Factoring Quadratic Equations Worksheet

    Oct 17, 17 05:34 PM

    Factoring quadratic equations worksheet-get some practice factoring quadratic equations

    Read More

New math lessons

Your email is safe with us. We will only use it to inform you about new math lessons.

            Follow me on Pinterest


Page copy protected against web site content infringement by Copyscape





Recent Lessons

  1. Factoring Quadratic Equations Worksheet

    Oct 17, 17 05:34 PM

    Factoring quadratic equations worksheet-get some practice factoring quadratic equations

    Read More

  Our Top Pages

Formula for percentage

Compatible numbers

Basic math test

Basic math formulas

Types of angles

Math problem solver

Algebra word problems

Surface area of a cube

Finding the average 

Scale drawings

Tough Algebra Word Problems.

If you can solve these problems with no help, you must be a genius!


Everything you need to prepare for an important exam!

K-12 tests, GED math test, basic math tests, geometry tests, algebra tests. 


Real Life Math Skills

Learn about investing money, budgeting your money, paying taxes, mortgage loans, and even the math involved in playing baseball.

 Recommended

Scientific Notation Quiz

Types of Angles Quiz

Graphing Slope Quiz

Adding and Subtracting Matrices Quiz  

Factoring Trinomials Quiz 

Solving Absolute Value Equations Quiz  

Order of Operations Quiz