# 0.4 Rational expression concepts -- rational equations

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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:

$\frac{x}{8}=\frac{3}{8}$

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
$\frac{3}{{x}^{2}+\text{12}x+\text{36}}=\frac{4x}{{x}^{3}+{4x}^{2}-\text{12}x}$ Same problem we worked before, but now we are equating these two fractions, instead of subtracting them.
$\frac{3\left(x\right)\left(x-2\right)}{\left(x+6{\right)}^{2}\left(x\right)\left(x-2\right)}=\frac{4x\left(x+6\right)}{x\left(x+6{\right)}^{2}\left(x-2\right)}$ Rewrite both fractions with the common denominator.
$3x\left(x-2\right)=4x\left(x+6\right)$ Based on the rule above—since the denominators are equal, we can now assume the numerators are equal.
$3{x}^{2}–6x=4{x}^{2}+24x$ Multiply it out
${x}^{2}+30x=0$ What we’re dealing with, in this case, is a quadratic equation. As always, move everything to one side...
$x\left(x+30\right)=0$ ...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.
$\mathrm{x=}0$ or $\mathrm{x=}-30$ 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 $\frac{3}{{x}^{2}+\text{12}x+\text{36}}=\frac{4x}{{x}^{3}+{4x}^{2}-\text{12}x}$ . 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 $\frac{3}{{x}^{2}+\text{12}x+\text{36}}$ and $\frac{4x}{{x}^{3}+{4x}^{2}-\text{12}x}$ , the two graphs would intersect at one point only: the point when $x=–30$ .

#### Questions & Answers

How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
what is Nano technology ?
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?
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
why we need to study biomolecules, molecular biology in nanotechnology?
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
why?
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?
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
what does nano mean?
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
it is a goid question and i want to know the answer as well
Maciej
characteristics of micro business
Abigail
for teaching engĺish at school how nano technology help us
Anassong
How can I make nanorobot?
Lily
Do somebody tell me a best nano engineering book for beginners?
there is no specific books for beginners but there is book called principle of nanotechnology
NANO
how can I make nanorobot?
Lily
what is fullerene does it is used to make bukky balls
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
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