Basics Of Log Functions

Algebra Level 1

4 x = 0.5 \large 4^{x} = 0.5 Find out the value of x x that satisfies the equation above.

Try out my set Mathematical nightmares .


The answer is -0.5.

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41 solutions

Samarth Sangam
Aug 20, 2014

0.5 can be written as 1/2 and further 1/2 can be written as 2 1 { 2 }^{ -1 } .

So 4 x = 2 1 2 2 x = 2 1 { 4 }^{ x }={ 2 }^{ -1 }\\ { 2 }^{ 2x }={ 2 }^{ -1 } therefore x=-1/2

4^x= 1/2

2*4^x= 1

2*2^(2x) =1

2^(1+2x)= 2^0

So, 1+2x=0 or x=-1/2

Devendra Marghade - 6 years, 9 months ago

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this is an interesting solution though a bit lengthy....

Sohaib Nafis - 6 years, 9 months ago

Nice explanation

Rajshekhar Jeenkeri - 5 years, 10 months ago

FYI - To type equations in Latex, you just need to add \ ( \ ) around your math code. In this way, you don't have to use \quad all the time. I've edited your solution so that you can refer to it.

Great work with using Latex :)

Calvin Lin Staff - 6 years, 9 months ago

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Solution couldn't be typed

Anup MAG - 6 years, 9 months ago

nice answer ,dude

Pedro Silva - 6 years, 9 months ago

nice answer

padma vathi - 6 years, 9 months ago

Simple equation would tell me that if there is a multiple on the left side 4xX=.5 therefore .5 /4 = .125 is the reverse operation.

Geoffrey Alan - 6 years, 9 months ago

I got .125 which was rejected as incorrect. Don't. get it and yes 4x.125 = .5 or 1/2

Geoffrey Alan - 6 years, 9 months ago

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power of not multiply

Justin Tay - 6 years, 9 months ago

It is not 4x = .5 it it 4 to the power of x = .5 4^x=.5 so your logic of dividing is incorrect, if anything you would take the square root of .5 with respect to x or even .5 to the power of 1/x which looks like: .5^(1/x)

Skyler Vertner - 5 years, 10 months ago

smart boy.

Danish Hafeez - 5 years, 10 months ago

THANKsssssssssssssssssss

Amal Amlu - 5 years, 9 months ago

This one is Really, Really basic logarithms & exponentials, and almost to trivial to bother with!!

Dale Wood - 4 years, 8 months ago

i find the contradict solution for this question is to find x value : 4 ^ 1/8 = .5 so x = 1/8 and tat is .125

Karthik Dawdler - 6 years, 6 months ago

Formatting failed

Benjamin Wong - 6 years, 9 months ago
Uahbid Dey
Sep 1, 2014

4 x = 2 2 x 4^{x}=2^{2x} 0.5 = 1 2 = 2 1 0.5=\frac{1}{2}=2^{-1} = > 2 x = 1 => 2x=-1 = > x = 1 2 => x = -\frac{1}{2} o r or 4 x = 0.5 4^{x}=0.5 = > x log 4 = log 0.5 => x\log 4 = \log 0.5 = > x = log 0.5 log 4 = 0.5 => x=\frac{\log 0.5 }{\log 4}=-0.5

The correct answer but the wrong calculation. Should be log 0.5/log 4.

Geoffrey Alan - 6 years, 9 months ago

this is the correct way to solve it thank u

Dinesh Vhatte - 6 years, 9 months ago

Y o u r a n s w e r h a s b e e n e d i t e d t o t h e c o r r e c t c a l c u l a t i o n Your\quad answer \quad has \quad been \quad edited \quad to \quad the \quad correct \quad calculation

Ritu Roy - 6 years, 7 months ago

log not required

multiuply both sides by 4

you get

4 x + 1 { 4 }^{ x+1 } = = 0.5 × 4 =0.5\times4

so,

4 x + 1 { 4 }^{ x+1 } = 2 2

or,

2 2 x + 2 { 2 }^{ 2x+2 } = 2 1 { 2 }^{ 1 }

now, we solve for x

2 x + 2 = 1 2x+2=1

2 x = 1 2x=-1

x = 1 2 x=\frac { -1 }{ 2 }

x = 0.5 x=\boxed{ -0.5 }

"log not required" is a quaint statement because nearly any logarithm problem can be converted into an exponential problem, and vice-versa. That is at the root of the two ideas because exponentials and logarithms are defined to be inverse functions of each other. Hence, a basic thing to do is to find the easiest (or easier) way to solve the problem.

Dale Wood - 4 years, 8 months ago

log 0.5 log 4 = 0.5 \frac { \log { 0.5 } }{ \log { 4 } } =\boxed{-0.5}

Finally figured it out using calculator but still struggle to figure out what is really going on.Good answer though Thomas.

Geoffrey Alan - 6 years, 9 months ago
Shovon Pramanik
Aug 24, 2014

4^x =0.5 or 2^2x=1/2 or 2^2x=2^-1 or x=-0.5

but 4^1/2 =root 4 =2

libi binu - 6 years, 9 months ago
Ta3iapxHs .
Dec 11, 2015

For those saying that calculating log(0.5)/log(4) requires a calculator.

log(0.5)=log(1/2)=log1-log2=-log2

And,

log(4)=log(2^2)=2log2

So,

log(0.5)/log(4)=-log2/(2log2)=-1/2

Mohammed Shams
Aug 30, 2014

since 4^(x) = 0.5 2^(2x)=1/2 2^(2x+1)=1 therefore 2x+1=0 2x=-1 x=-0.5

Mahedi Prince
Aug 21, 2014

{ 2 }^{ 2x }={ 2 }^{ -1 } =>2x=-1 =>x=-.5

Benjamin Wong
Aug 21, 2014

1/sqrt(4) = 0.5, therefore x= -(1/2)

Anshu Garg
Dec 9, 2016

CORRECT ANSWER IS

-0.5

Praveen Murugesan
Jun 14, 2016

Take log on both side X log 4= log 0.5;
X=log .5/log 4;
X=-1/2. But its long version

Pbkanita Mata
May 23, 2016

4^x=0.5we can take both side x so,

  4^2x=0.5^x    
 (2^x) ^2=0.5^x          
 Now send 2^x to RHS and x will be left over
    x=(-2+0.5)^x
     x=-0.5

Your solution is not easy to follow. Could you please explain how you got from ( 2 x ) 2 = 0. 5 x (2^x) ^2=0.5^x to x = ( 2 + 0.5 ) x x=(-2+0.5)^x ?

Pranshu Gaba - 5 years ago
Joji Thomas
Apr 12, 2016

0.5=1/2 4^x=0.5 So, first we have to write 4^x in terms of 2 putting x=1/2, we get 2 We have to make it 182, so negative exponent of x gives 0.5 -x=1/2 x=-1/2=-0.5

Miguel Galang
Jan 13, 2016

2(4^x)=2(.5)

2(4^x)=1

first make it 1 then

1 / 2 = .5 and negative since it is an exponent. solve it this way. may be wrong

\sqrt{x}= x^{1/2}

0.5 = 1 / 2

4^{x} = 1/ 4^{-x}

1/2 = 1/4 ^{-1/2}

Ramesh Jayaraman
Dec 25, 2015

=> 2^2x = 2 ^ -1 => x=-0.5

Joshua Chin
Sep 4, 2015

4=2^2

so 4x = 2^2x = 0.5

0.5 = 1/2 which is reciprocal of 2 so 2x = -1

x = -0.5

Brandt Ozawa
Aug 31, 2015

x(log(4)) = log(0.5)

x = log(0.5) / log(4)

x = -0.5

Akash Papnai
Aug 21, 2015

4^x=0.5 4^x=1÷2 2 4^x=1 2 2^2x=2^0 2^(2x+1)=2^0 2x+1=0 X=-0.5

Rishi Jaientilal
Jul 13, 2015

I admit i used the calculator. I was trying without using the calc mas some steps were missing. What can I do from -1 X log4 (2) = x?

Actually u can change d base 4 to 2^2. then take the inverse of this power(in this case 2 to multiply the log. -1x log4 (2) = -1x log2^2 (2) = -1x ½ x log2 (2) = -1 x ½= -½ Remember log2 (2)=1 .tanx

Joseph Eze - 5 years, 7 months ago
Alex James
Jul 10, 2015

You can use ln to separate x using log rules.

ln4^x = ln0.5

xln4 = ln0.5 (Use log rule that logA^B = BlogA)

x = ln0.5/ln4 (Requires calculator)

x=-0.5

Actually In0.5/In4 can b solved without a calculator using d change of base method. In0.5/In4 = In4 (0.5) = In4 (2^—¹) = -1 x In4 (2) = -1 x In2^2 (2) = -1 x ½ In2 (2) = -1 x ½ = -½

Joseph Eze - 5 years, 7 months ago
Jasvinder Singh
Dec 14, 2014

multiply both sides by 4 ,,, so ,,,:-4 /\x+1=2,,, 4/\x+1=4/\1/2,,, x+1=1/2,,, x=-1/2

Deepak Sikarwar
Dec 14, 2014

4^x=0.5,, 2^2x=2^-1,,

2x=-1,, x=-0.5

Ravesh Kumar
Dec 14, 2014

FIRST METHOD taking LOG in both sides, x log4 = log(1/2) x =log (1/2)/log4 having common base 2, then x =log4(1/2) (here 4 is base). =-1/2 =-0.5 second method is basics of surds.

Ahaan Rungta
Dec 14, 2014

Note that 0.5 = 1 2 = 1 2 1 = 2 1 = ( 2 2 ) 1 2 = 4 0.5 . 0.5 = \frac {1}{2} = \frac {1}{2^1} = 2^{-1} = \left( 2^2 \right)^{-\frac{1}{2}} = 4^{\boxed{-0.5}}.

Sagar Supeda
Nov 14, 2014

4^x=.5 x=log(0.5)/log(4)

Chuong Thanh
Nov 3, 2014

S i n e : 0.5 = 4 1 2 s o = > 4 x = 4 1 2 Sine: 0.5 = 4^{-\frac{1}{2}} so => 4^{x} = 4^{-\frac{1}{2}} = > T h e r e f o r e : x = 1 2 = 0.5 => Therefore: x = -\frac{1}{2} = \boxed{-0.5} !!!

Efraim Gunawan
Oct 2, 2014

4^x = 0.5

x = 4 log 1/2

= 2^2 log 2^-1 {sesuai sifat a^m log b^n = m/n(a log b)}

x = -1/2 = - 0.5

Jaswanth Varma
Sep 21, 2014

We can do this using logarithms too. We know that a ^ x = y implies x = log(y) to the base "a" . Here a=4 and y=0.5=1/2=2^(-1). So x = log(2 ^ ( -1)) to the base log(4). So x = -log(2)/log(4). So x = -log(2) / 2 * log(2) = -1/2 = -0.5

Albi Chrsto
Sep 16, 2014

4 x = 0.5 4^{x} = 0.5
0.5 = 1 / 2 = 2 1 0.5= 1/2 =2^{-1}
4 x = 2 2 x 4^{x} = 2^{2x}
=> 2x= -1
=> x= -1/2 = -0.5



Swetank Patel
Sep 14, 2014

take log both side and get ans x log 4=log .5 x=-.5

4^x=1/2, take log to the base 2 on both sides, =>xlog 2^2=log 1 -log 2, 2x log 2= 0 - log2, 2x=-1, x=-0.5, here the base of the log is 2

Taking ln both side of the eqn. ln 4^x=ln(0.5), xln(4)=ln(0.5), x=ln(0.5)/ln(4), x=-0.5

Satyam Singh
Aug 31, 2014

ln4^x=ln(1/2) (Taking log both sides) ln 2^2x = ln 2^-1 2x ln2=-1ln2 now, 2x=-1 x=-1/2=-0.5

4 ^ (- x ) =1 / ( 4 ^ x ) -> 4 ^ 0. 5 = 2 -> 0.5 = 1/ 2 -> 4 ^ (-0.5) = 1 / ( 4 ^ 0.5 ) = 1 / 2 = 0.5

Ka Kei Yeung
Aug 31, 2014

Since it belongs to the category of Logarithms, let's try it using log (whichever base). x*log(4)=log(0.5) x=log(4)/log(0.5) =-0.5

Shashank Kris
Aug 31, 2014

we know that a^b=x then->log x to the base a=b log 0.5 to the base 4=x =>log(1/2)/log 4=x =>(log1-log2)/log 4)=x =>(0-1)/2log2=x (log x^b=blog x) =>-1/2=x

Piwai Zaranyika
Aug 31, 2014

Xlog4=log0.5

x=log0.5/log4

=-0.5

Rakesh Geddam
Aug 30, 2014

log0.5/log4

Abhishek Sheopory
Aug 22, 2014

x = log0.5 / log4

Abhi Shek
Aug 21, 2014

take log on both sides and ul get, x=log(.5)/log(4)

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