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Working rules : We shall be using following definitions/results for solving problems in this module :

  • y = log a x , where a > 0, a 1, x > 0, y R
  • y = log a x x = a y
  • If log a x y , then x a y , if a > 1
  • If log a x y , then x a y , if a < 1

Domain of different logarithmic functions

Problem : Find the domain of the function given by (Be aware that "x" appears as base of given logrithmic function):

f x = log x 2

Solution : By definition of logarithmic function, we know that base of logarithmic function is a positive number excluding x =1.

x > 0, x 1

Hence, domain of the given function is :

Domain of the function

Thick line represents domain of the given function.

Domain = 0, { 1 }


Domain = 0,1 { 1, }

Problem : Find the domain of the function given by :

f x = log 10 x 2 5 x + 6 x 2 + 5 x + 9

Solution : The argument (input to the function) of logarithmic function is a rational function. We need to find values of “x” such that the argument of the function evaluates to a positive number. Hence,

x 2 5 x + 6 x 2 + 5 x + 9 > 0

In this case, we can not apply sign scheme for the rational function as a whole. Reason is that the quadratic equation in the denominator has no real roots and as such can not be factorized in linear factors. We see that discreminant,"D", of the quadratic equation in the denominator, is negative :

D = b 2 4 a c = 5 2 4 X 1 X 9 = 25 36 = - 11

The quadratic expression in denominator is positive for all value of x as coefficient of squared term is positive. Clearly, sign of rational function is same as that of quadratic expression in the numerator. The coefficient of squared term of the numerator “ x 2 ”, is positive for all values of “x”. The quadratic expression in the numerator evaluates to positive for intervals beyond root values. The roots of the corresponding equal equation is :

x 2 2 x 3 x + 6 = 0 x x 2 3 x 2 = 0 x 2 x 3 = 0

Domain of the function

Thick line represents domain of the given function.

x < 2 or x > 3

Domain = ( - , 2 ) ( 3, )

Problem : Find the domain of the function given by :

f x = log 10 6 x x 2 8

Solution : The function is a square root of a logarithmic function. On the other hand argument of logarithmic function is a rational function. In order to find the domain of the given function, we first determine what values of “x” are valid for logarithmic function. Then, we apply the condition that expression within square root should be non-negative number. Domain of given function is intersection of intervals of x obtained for each of these conditions. Now, we know that argument (input to function) of logarithmic function is a positive number. This implies that we need to find the interval of “x” for which,

6 x x 2 8 > 0

6 x x 2 > 0

In above step, we should emphasize here that we multiply “8” and “0” and retain the inequality sign because 8>0. Now, we multiply the inequality by “-1”. Therefore, inequality sign is reversed.

x 2 6 x < 0

Here, roots of corresponding quadratic equation “ x 2 6 x ” is x = 0, 6. It means that middle interval between “0 and 6” is negative as coefficient of “ x 2 ” is positive i.e. 6>0. Hence, interval satisfying the inequality is :

Domain of the function

Thick line represents domain of the given function.

Questions & Answers

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.
yes that's correct
I think
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
how nano science is used for hydrophobicity
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
what is differents between GO and RGO?
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
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
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
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
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
Sneha Reply

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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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