<< Chapter < Page Chapter >> Page >

Finding inverses of rational functions

As with finding inverses of quadratic functions, it is sometimes desirable to find the inverse of a rational function , particularly of rational functions that are the ratio of linear functions, such as in concentration applications.

Finding the inverse of a rational function

The function C = 20 + 0.4 n 100 + n represents the concentration C of an acid solution after n mL of 40% solution has been added to 100 mL of a 20% solution. First, find the inverse of the function; that is, find an expression for n in terms of C . Then use your result to determine how much of the 40% solution should be added so that the final mixture is a 35% solution.

We first want the inverse of the function in order to determine how many mL we need for a given concentration. We will solve for n in terms of C .

C = 20 + 0.4 n 100 + n C ( 100 + n ) = 20 + 0.4 n 100 C + C n = 20 + 0.4 n 100 C 20 = 0.4 n C n 100 C 20 = ( 0.4 n C ) n n = 100 C 20 0.4 C

Now evaluate this function at 35%, which is C = 0.35.

n = 100 ( 0.35 ) 20 0.4 0.35 = 15 0.05 = 300

We can conclude that 300 mL of the 40% solution should be added.

Got questions? Get instant answers now!
Got questions? Get instant answers now!

Find the inverse of the function f ( x ) = x + 3 x 2 .

f 1 ( x ) = 2 x + 3 x 1

Got questions? Get instant answers now!

Key concepts

  • The inverse of a quadratic function is a square root function.
  • If f 1 is the inverse of a function f , then f is the inverse of the function f 1 . See [link] .
  • While it is not possible to find an inverse of most polynomial functions, some basic polynomials are invertible. See [link] .
  • To find the inverse of certain functions, we must restrict the function to a domain on which it will be one-to-one. See [link] and [link] .
  • When finding the inverse of a radical function, we need a restriction on the domain of the answer. See [link] and [link] .
  • Inverse and radical and functions can be used to solve application problems. See [link] and [link] .

Section exercises

Verbal

Explain why we cannot find inverse functions for all polynomial functions.

It can be too difficult or impossible to solve for x in terms of y .

Got questions? Get instant answers now!

Why must we restrict the domain of a quadratic function when finding its inverse?

Got questions? Get instant answers now!

When finding the inverse of a radical function, what restriction will we need to make?

We will need a restriction on the domain of the answer.

Got questions? Get instant answers now!

The inverse of a quadratic function will always take what form?

Got questions? Get instant answers now!

Algebraic

For the following exercises, find the inverse of the function on the given domain.

f ( x ) = ( x 4 ) 2 ,   [ 4 , )

f 1 ( x ) = x + 4

Got questions? Get instant answers now!

f ( x ) = ( x + 2 ) 2 ,   [ −2 , )

Got questions? Get instant answers now!

f ( x ) = ( x + 1 ) 2 3 ,   [ −1 , )

f 1 ( x ) = x + 3 1

Got questions? Get instant answers now!

f ( x ) = 3 x 2 + 5 , ( , 0 ]

f 1 ( x ) = x 5 3

Got questions? Get instant answers now!

f ( x ) = 12 x 2 ,   [ 0 , )

Got questions? Get instant answers now!

f ( x ) = 9 x 2 ,   [ 0 , )

f ( x ) = 9 x

Got questions? Get instant answers now!

f ( x ) = 2 x 2 + 4 ,   [ 0 , )

Got questions? Get instant answers now!

For the following exercises, find the inverse of the functions.

f ( x ) = x 3 + 5

f −1 ( x ) = x 5 3

Got questions? Get instant answers now!

f ( x ) = 4 x 3

f 1 ( x ) = 4 x 3

Got questions? Get instant answers now!

For the following exercises, find the inverse of the functions.

f ( x ) = 2 x + 1

f −1 ( x ) = x 2 1 2 , [ 0 , )

Got questions? Get instant answers now!

f ( x ) = 9 + 4 x 4

f −1 ( x ) = ( x 9 ) 2 + 4 4 , [ 9 , )

Got questions? Get instant answers now!

Questions & Answers

what is biology
Hajah Reply
the study of living organisms and their interactions with one another and their environments
AI-Robot
what is biology
Victoria Reply
HOW CAN MAN ORGAN FUNCTION
Alfred Reply
the diagram of the digestive system
Assiatu Reply
allimentary cannel
Ogenrwot
How does twins formed
William Reply
They formed in two ways first when one sperm and one egg are splited by mitosis or two sperm and two eggs join together
Oluwatobi
what is genetics
Josephine Reply
Genetics is the study of heredity
Misack
how does twins formed?
Misack
What is manual
Hassan Reply
discuss biological phenomenon and provide pieces of evidence to show that it was responsible for the formation of eukaryotic organelles
Joseph Reply
what is biology
Yousuf Reply
the study of living organisms and their interactions with one another and their environment.
Wine
discuss the biological phenomenon and provide pieces of evidence to show that it was responsible for the formation of eukaryotic organelles in an essay form
Joseph Reply
what is the blood cells
Shaker Reply
list any five characteristics of the blood cells
Shaker
lack electricity and its more savely than electronic microscope because its naturally by using of light
Abdullahi Reply
advantage of electronic microscope is easily and clearly while disadvantage is dangerous because its electronic. advantage of light microscope is savely and naturally by sun while disadvantage is not easily,means its not sharp and not clear
Abdullahi
cell theory state that every organisms composed of one or more cell,cell is the basic unit of life
Abdullahi
is like gone fail us
DENG
cells is the basic structure and functions of all living things
Ramadan
What is classification
ISCONT Reply
is organisms that are similar into groups called tara
Yamosa
in what situation (s) would be the use of a scanning electron microscope be ideal and why?
Kenna Reply
A scanning electron microscope (SEM) is ideal for situations requiring high-resolution imaging of surfaces. It is commonly used in materials science, biology, and geology to examine the topography and composition of samples at a nanoscale level. SEM is particularly useful for studying fine details,
Hilary
cell is the building block of life.
Condoleezza Reply
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply
Practice Key Terms 1

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play Download on the App Store Now




Source:  OpenStax, Algebra and trigonometry. OpenStax CNX. Nov 14, 2016 Download for free at https://legacy.cnx.org/content/col11758/1.6
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Algebra and trigonometry' conversation and receive update notifications?

Ask