Associated Topics || Dr. Math Home || Search Dr. Math

### Horizontal and Vertical Asymptotes

```
Date: 12/5/95 at 3:14:42
From: Anonymous
Subject: question

Dr. Math:

I am a Math 12 student.  I am confused about the horizontal
asymptotes and the vertical asymptotes.  Please tell me how to find
them, and their definition.

Thank you very much.

Yours truly

David Ju
```

```
Date: 1/5/96 at 10:44:35
From: Doctor Ethan
Subject: Re: question

Hey David,

Great Question.  And I even think that I have an answer for you.

Whenever a function seems to get infinitely close to a line without
ever crossing it, then that line is a an asymptote.  For example y=1/x

Do you know what it looks like?  I hope so.

It has two asymptotes.  One is vertical and one is horizontal.

That is because 1/x for very large x will get close and closer to 0.
However, it will never be zero.  So the line y=0 is an asymptote.

In the same way, as x gets close to zero, 1/x gets huge.  In fact it
can get as big as you want.  Formally, when this happens mathematicians
say that the limit of 1/x as x approaches zero is infinity. So in
this case the line x=0 is an asymptote.

Now they do get more complex but the general idea is this:
with any x value, where the limit approaches infinity you have a
vertical asymptote.

Whatever value the function approaches as the x value goes to infinity
is where the horizontal asymptote is.

Let's do one more example.

4
-----
(x-2)

Let's start by letting x get really big.  When x gets big, what
does the value of the whole thing go toward?

Well 4/(very big number) is going to be very close to zero.
So again we are going to have a horizontal asymptote at zero.

Let's look for vertical asymptotes.

We need to find where the value of the function goes to infinity.
Do you see why that will be the same places where the bottom goes
toward zero?

See if you can find those places and they will be the vertical
asymptotes.

Hope this helps, David.

-Doctor Ethan,  The Geometry/Math Forum

```
Associated Topics:
High School Basic Algebra
High School Definitions

Search the Dr. Math Library:

 Find items containing (put spaces between keywords):   Click only once for faster results: [ Choose "whole words" when searching for a word like age.] all keywords, in any order at least one, that exact phrase parts of words whole words

Submit your own question to Dr. Math
Math Forum Home || Math Library || Quick Reference || Math Forum Search

Ask Dr. MathTM
© 1994- The Math Forum at NCTM. All rights reserved.
http://mathforum.org/dr.math/