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Inequality is an important concept in understanding function and its properties – particularly domain and range. Many function forms are valid in certain interval(s) of real numbers. This means definition of function is subjected to certain restriction of values with respect to dependent and independent variables. The restriction is generally evaluated in terms of algebraic inequalities, which may involve linear, quadratic, higher degree polynomials or rational polynomials.

Function definition and inequality

A function imposes certain limitations by virtue of definition itself. We have seen such restriction with respect to radical functions in which polynomial inside square root needs to be non-negative. We have also seen that denominator of a rational function should not be zero. We shall learn about different functions in subsequent modules. Here, we consider few examples for illustration :

1 : f x = log a 3 x 2 x + 4

Here, logrithmic function is defined for a 0,1 1, and

3 x 2 x + 4 > 0

2 : f x = arcsin 3 x 2 x + 4

Here, arcsine function is defined in the domain [-1,1]. Hence,

- 1 3 x 2 x + 4 1

It is clear that we need to have clear understanding of algebraic inequalities as function definitions are defined with certain condition(s).

Forms of function inequality

Function inequality compares function to zero. There are four forms :

1 : f(x)<0

2 : f(x) ≤ 0

3 : f(x)>0

4 : f(x) ≥ 0

Here, f(x)<0 and f(x)>0 are strict inequalities as they confirm the notion of “less than” and “greater than”. There is no possibility of equality. If a strict inequality is true, then non-strict equality is also true i.e.

1 : If f(x)>0 then f(x) ≥ 0 is true.

2 : If f(x) ≥ 0 then f(x)>0 is not true.

3 : If f(x)<0 then f(x) ≤ 0 is true.

4 : If f(x) ≤ 0 then f(x)<0 is not true.

Further, we may be presented with inequality which compares function to non-zero value :

3 x 2 x - 4

However, such alterations are equivalent expressions. We can always change this to standard form which compares function with zero :

3 x 2 x + 4 > 0

Inequalities

Some important definitions/ results are enumerated here :

  • Inequalities involve a relation between two real numbers or algebraic expressions.
  • The inequality relations are "<", ">", "≤" and "≥".
  • Equal numbers can be added or subtracted to both sides of an inequality.
  • Both sides of an inequality can be multiplied or divided by a positive number without any change in the inequality relation.
  • Both sides of an inequality can be multiplied or divided by a negative number with reversal of inequality relation.
  • Both sides of an inequality can be squared, provided expressions are non-negative. As a matter of fact, this conclusion results from rule that we can multiply both sides with a positive number.
  • When both sides are replaced by their inverse, the inequality is reversed .

Equivalently, we may state above deductions symbolically.

If x > y , then :

x + a > y + a

a x > a y ; a > 0

a x < a y ; a < 0

x 2 > y 2 ; x , y > 0

1 x < 1 y ; when “x” and “y” have same sign.

It is evident that we can deduce similar conclusions with the remaining three inequality signs.

Intervals with inequalities

In general, a continuous interval is denoted with "less than (<)" or "less than equal to (≤)" inequalities like :

1 < x 5

The segment of a real number line from a particular number extending to plus infinity is denoted with “greater than” or “greater than equal to” inequalities like :

x 3

The segment of real number line from minus infinity to a certain number on real number line is denoted with “less than(<) or less than equal to (≤)” inequalities like :

x - 3

Two disjointed intervals are combined with “union” operator like :

1 < x 2 x > 5

Linear inequality

Linear function is a polynomial of degree 1. A linear inequality can be solved for intervals of valid “x” and “y” values, applying properties of inequality of addition, subtraction, multiplication and division. For illustration, we consider a logarithmic function, whose argument is a linear function in x.

f x = log e 3 x + 4

The argument of logarithmic function is a positive number. Hence,

x > - 4 3

Therefore, interval of x i.e. domain of logarithmic function is - 4 / 3, . The figure shows the values of “x” on a real number line as superimposed on x-axis. Note x= - 4/3 is excluded.

Graph of logarithmic function

Domain is traced on x-axis.

When f(x) = 0,

3 x + 4 = e f x = e 0 = 1

x = - 1

It means graph intersects x-axis at x=-1 as shown in the figure. From the figure, it is clear that range of function is real number set R.

We shall similarly consider inequalities involving polynomials of higher degree, rational function etc in separate modules.

Problem : A linear function is defined as f(x)=2x+2. Find valid intervals of “x” for each of four inequalities viz f(x)<0, f(x) ≤ 0, f(x)>0 and f(x) ≥ 0.

Solution : Here, given function is a linear function. At y=0,

f x = 2 x + 2 = 0

x = - 1

At x=0,

f x = 2

We draw a line passing through these two points as shown in the figure. From the figure, we conclude that :

Graph of linear function

Graph is continuous for all values of x.

f x < 0 ; x - , - 1

f x 0 ; x ( - , - 1 ]

f x > 0 ; x - 1,

f x 0 ; x [ - 1, )

Questions & Answers

where we get a research paper on Nano chemistry....?
Maira Reply
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
Ali
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
Google
da
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Bhagvanji
hey
Giriraj
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
revolt
da
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
ya I also want to know the raman spectra
Bhagvanji
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
Nasa has use it in the 60's, copper as water purification in the moon travel.
Alexandre
nanocopper obvius
Alexandre
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
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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What is power set
Satyabrata Reply
Period of sin^6 3x+ cos^6 3x
Sneha Reply
Period of sin^6 3x+ cos^6 3x
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Source:  OpenStax, Functions. OpenStax CNX. Sep 23, 2008 Download for free at http://cnx.org/content/col10464/1.64
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