What is a one-to-one function?

In this ar we’ll talk around how to identify whether a graph to represent a one-to-one function.

You are watching: One to one vertical line test

If a relationship is a function, then it has precisely one ???y???-value because that each ???x???-value. If a role is one-to-one, it likewise has specifically one ???x???-value because that each ???y???-value.


The factor we care about one-to-one features is due to the fact that only a one-to-one duty has an inverse. If the duty is no one-to-one, then part restrictions could be necessary on the domain of the role to make it invertible.

The an initial way we’ll look at even if it is or not a duty is one-to-one is utilizing the Horizontal heat Test.

One-to-one functions with the horizontal heat test

Remember the we’ve already talked about the Vertical heat Test, i beg your pardon is a test we usage to tell united state whether or not a graph to represent a function. Any function passing the Vertical line Test can only have one distinct output worth ???y???for any single input value ???x???.

In the same means that the Vertical line Test tells us whether or no a graph is a function, the Horizontal line Test tells united state whether or not a duty is one-to-one.

The graph below passesthe Horizontal line Test because a horizontal heat cannot crossing it an ext than once.


Basically, the Horizontal heat Test claims that no ???y???-value coincides to two different ???x???values. If a function passes the Horizontal line Test, climate no horizontal line will cross the graph an ext than once, and the graph is stated to it is in one-to-one.

This graphdoesn"t happen the Horizontal heat Test because any kind of horizontal line between ???y=-2???and ???y=2???would crossing it an ext than once.


All non-horizontal linear attributes are one-to-one because a horizontal line attracted anywhere will just pass v once. A look in ~ this following graph tells united state that there’s no horizontal line the intersects the graph at an ext than one point, so the relation is a function.


On the other hand, quadratic features are never ever one-to-one. A look at the next graph mirrors us that it’s simple to find a horizontal line that intersects the graph at much more than point, thereby proving the the function is no one-to-one.


This is one factor it’s a an excellent idea to have an idea of what duty families look like. If you’re familiar with what a group of functions look like, then you can think around the graph in her head to decide if it’s a one-to-one function. For example, quadratics form a “u” form so a horizontal line would certainly pass through the graph twice. That means quadratic functions are never one-to-one.

One-to-one functions algebraically

Another an approach to inspect for a one-to-one function is come think that ???f(a)=f(b)??? indicates ???a=b???in a one-to-one function.

Say we want to know if ???f(x)=sqrtx-2???is one-to-one without illustration or visualizing the graph.

Then we think if ???f(a)=f(b)???then ???a=b???and the duty is one-to-one. We know that ???f(a)=sqrta-2???and ???f(b)=sqrtb-2???, for this reason we can say



???left(sqrta-2 ight)^2=left(sqrtb-2 ight)^2???



So ???f(x)???is a one-to-one function.

How to use the Horizontal line Test to determine whether or not a function is one-to-one

" data-provider-name="Wistia, Inc.">

Take the course

Want come learn much more about Algebra 2? I have a step-by-step course for that. :)

Learn much more

Showing the the function is 1-to-1


Show that the role is one-to-one by showing ???f(a)=f(b)???leads come ???a=b???.


We’ll begin by replacing ???x???with ???a???, and then setting that equal to whatever we gain when we replace ???x???with ???b???.







This method ???f(x)???is a one-to-one function.

Let’s try another example.

On the various other hand, quadratic attributes are never one-to-one.


Show that ???g(x)???is not one-to-one by mirroring that ???f(a)=f(b)???does not suggest that ???a=b???.

See more: Which Four Elements Make Up Approximately 96 Of Living Matter


All we require is one instance to present that ???f(a)=f(b)???does not indicate that ???a=b???. That way we can pick one example where ???f(a)=f(b)???but ???a eq b???. Think about the instance when ???a=2???and ???b=-2???, then ???a eq b???but




Therefore, ???f(2)=f(-2)???but ???2 eq -2???. Due to the fact that we’ve uncovered one case, the role is not one-to-one.

Get accessibility to the complete Algebra 2 course

obtain started
find out mathKrista KingMay 12, 2021math, find out online, virtual course, virtual math, algebra, algebra 2, algebra ii, horizontal line test, one-to-one functions, 1-to-1 functions
Facebook0 Twitter LinkedIn0 Reddit Tumblr Pinterest0

Solving borders with conjugate method
find out mathKrista KingMay 13, 2021math, discover online, virtual course, virtual math, calculus, calculus 1, calculus i, solitary variable calculus, single variable calc, limits, limits and continuity, conjugate method, resolving limits, solving limits with conjugate method, conjugate technique for limits, conjugate
functional notation and examining functions
discover mathKrista KingMay 11, 2021math, discover online, digital course, virtual math, algebra, algebra 1, algebra i, practical notation, functions, examining functions
Online math courses