<< Chapter < Page Chapter >> Page >
This module introduces rational expressions in equations.

Rational equations

A rational equation means that you are setting two rational expressions equal to each other. The goal is to solve for x; that is, find the x value(s) that make the equation true.

Suppose I told you that:

x 8 = 3 8 size 12{ { {x} over {8} } = { {3} over {8} } } {}

If you think about it, the x in this equation has to be a 3. That is to say, if x=3 then this equation is true; for any other x value, this equation is false.

This leads us to a very general rule.

A very general rule about rational equations

If you have a rational equation where the denominators are the same, then the numerators must be the same.

This in turn suggests a strategy: find a common denominator, and then set the numerators equal.

Example: Rational Equation
3 x 2 + 12 x + 36 = 4x x 3 + 4x 2 12 x size 12{ { {3} over {x rSup { size 8{2} } +"12"x+"36"} } = { {4x} over {x rSup { size 8{3} } +4x rSup { size 8{2} } - "12"x} } } {} Same problem we worked before, but now we are equating these two fractions, instead of subtracting them.
3 ( x ) ( x 2 ) ( x + 6 ) 2 ( x ) ( x 2 ) = 4x ( x + 6 ) x ( x + 6 ) 2 ( x 2 ) size 12{ { {3 \( x \) \( x - 2 \) } over { \( x+6 \) rSup { size 8{2} } \( x \) \( x - 2 \) } } = { {4x \( x+6 \) } over {x \( x+6 \) rSup { size 8{2} } \( x - 2 \) } } } {} Rewrite both fractions with the common denominator.
3 x ( x - 2 ) = 4 x ( x + 6 ) Based on the rule above—since the denominators are equal, we can now assume the numerators are equal.
3 x 2 6 x = 4 x 2 + 24 x Multiply it out
x 2 + 30 x = 0 What we’re dealing with, in this case, is a quadratic equation. As always, move everything to one side...
x ( x + 30 ) = 0 ...and then factor. A common mistake in this kind of problem is to divide both sides by x ; this loses one of the two solutions.
x= 0 or x= -30 Two solutions to the quadratic equation. However, in this case, x = 0 is not valid, since it was not in the domain of the original right-hand fraction. (Why?) So this problem actually has only one solution, x = 30 .

As always, it is vital to remember what we have found here. We started with the equation 3 x 2 + 12 x + 36 = 4x x 3 + 4x 2 12 x size 12{ { {3} over {x rSup { size 8{2} } +"12"x+"36"} } = { {4x} over {x rSup { size 8{3} } +4x rSup { size 8{2} } - "12"x} } } {} . We have concluded now that if you plug x = 30 into that equation, you will get a true equation (you can verify this on your calculator). For any other value, this equation will evaluate false.

To put it another way: if you graphed the functions 3 x 2 + 12 x + 36 size 12{ { {3} over {x rSup { size 8{2} } +"12"x+"36"} } } {} and 4x x 3 + 4x 2 12 x size 12{ { {4x} over {x rSup { size 8{3} } +4x rSup { size 8{2} } - "12"x} } } {} , the two graphs would intersect at one point only: the point when x = 30 .

Questions & Answers

what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
learn
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
learn
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
research.net
kanaga
sciencedirect big data base
Ernesto
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Privacy Information Security Software Version 1.1a
Good
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get the best Algebra and trigonometry course in your pocket!





Source:  OpenStax, Rational expressions. OpenStax CNX. Feb 28, 2011 Download for free at http://cnx.org/content/col11278/1.2
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Rational expressions' conversation and receive update notifications?

Ask