Manipulation of Indices

Algebra Level 1

8 m = 27 , 4 m = ? \LARGE 8^{ \color{#3D99F6} m } =27, \ \ \ \ \ \ \ 4^{ \color{#3D99F6} m} = \ ?


The answer is 9.

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30 solutions

Tom Gallagher
Feb 4, 2015

8 m = ( 2 3 ) m = 2 3 m 8^m=(2^3)^{m} = 2^{3m}

4 m = ( 2 2 ) m = 2 2 m 4^m=(2^2)^{m} = 2^{2m}


2 3 m = 27 2^{3m} = 27

2 m = 27 3 = 3 \therefore 2^m = \sqrt[3]{27} = 3


2 2 m = ( 2 m ) 2 2^{2m}= (2^m)^{2}

2 2 m = 3 2 = 9 2^{2m} = 3^2 = 9

8 m = 27 2 3 ( m ) = 3 3 ( 3 i n b o t h ) 2 m = 3 ( s q u a r e ) 2 2 m = 3 2 4 m = 9 { 8 }^{ m }\quad =\quad 27\\ { 2 }^{ 3(m) }\quad =\quad { 3 }^{ 3 }\quad \quad (\sqrt [ 3 ]{ } in\quad both)\\ { 2 }^{ m }\quad =\quad 3\quad \quad \quad \quad (square)\\ { 2 }^{ 2m }\quad =\quad { 3 }^{ 2 }\\ { 4 }^{ m }\quad =\quad 9

Thiago Martinoni - 6 years, 4 months ago

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this is really helpful

Aysha Anam - 6 years, 4 months ago

totally agreed bro...congratzzz

Sumit Sehwag - 6 years, 3 months ago

Easy and nice method...

Shruti Agarwal - 5 years, 4 months ago

esse é meu namorado, parabéns, gostei muito daquela parte com números ... adorei <3

Gabrielle Giordano - 6 years, 3 months ago

amazing bro

anim listowell - 5 years, 6 months ago

Great at Solution

Shajan Sha - 4 years, 7 months ago

NICE one Dude

Soumik Saha - 5 years, 4 months ago

That's exactly what I did. Nice problem by the way.

Oussama Boussif - 6 years, 4 months ago

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Thank you :')

Tom Gallagher - 6 years, 4 months ago

Thanx a lot for making it clear to me

Gouri Asnani - 5 years, 8 months ago

can you give me a easier way

Yash Singh - 5 years, 5 months ago

Take log on both sides its easy

Akash Kumar - 5 years, 3 months ago

Nice solution. Like it

Christy Mathew - 5 years ago

Very easy to understand

Katie Mai - 4 years, 10 months ago

4 m = ( 8 2 3 ) m = ( 8 m ) 2 3 = 27 2 3 = 9 It is given that 8 m = 27 4^m = (8^{\frac{2}{3}})^m = (\color{#3D99F6}{8^m})^{\frac{2}{3}} = \color{#3D99F6}{27}^{\frac{2}{3}} = \boxed{9} \quad \quad \color{#3D99F6}{\text{It is given that }8^m = 27}

In response to Chew-Seong Cheong: Your explaination was easy to understand.

Astom Hazara - 5 years, 5 months ago

Wow!! Great explanation

Katie Mai - 4 years, 10 months ago

Short and sweet.

Niranjan Khanderia - 5 years, 9 months ago

I'm actually confused how we would go from the exponent 8^m to 27^2/3!

Refath Bari - 4 years, 11 months ago

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It is given that 8 m = 27 8^m = 27 .

Chew-Seong Cheong - 4 years, 11 months ago
Lu Chee Ket
Feb 5, 2015

To be honest, I actually used calculator for fast relieve.

4^(Ln 27/ Ln 8) = 9

Did the same, but without a calculator :D

Utkarsh Singh - 6 years, 4 months ago

Mee too :D

Hoang Le - 5 years, 7 months ago

8 m = 27 ( 2 m ) 3 = 3 3 ( 2 m ) 2 = 3 2 I m p l i e s 4 m = 9. \large 8^m=27\\ \implies (2^m)^3= 3^3 \\\therefore (2^m)^2=3^2~~~~~\\Implies~~~~4^m=9.

different approach. Nice. Keep it up.

Venkataraman Gopalan - 5 years, 9 months ago

Gud man......great

Himanshu Sidana - 5 years, 5 months ago

this is what i am looking for! thnks.

Satsky Guard - 5 years ago

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You are welcome.

Niranjan Khanderia - 5 years ago
Daniel Ferreira
Feb 7, 2015

8 m = 27 log 8 27 = m m = 1 3 3 log 2 3 m = log 2 3 8^m = 27 \\\\ \log_8 27 = m \\\\ m = \frac{1}{3} \cdot 3 \cdot \log_2 3 \\\\ \boxed{m = \log_2 3}

Consideremos 4 m = k 4^m = k , segue que:

log 4 k = m 1 2 log 2 k = log 2 3 log 2 k = 2 log 2 3 log 2 k = log 2 9 k = 9 4 m = 9 \log_4 k = m \\\\ \frac{1}{2} \cdot \log_2 k = \log_2 3 \\\\ \log_2 k = 2 \cdot \log_2 3 \\\\ \log_2 k = \log_2 9 \\\\ k = 9 \\\\ \boxed{\boxed{4^m = 9}}

Same method I used! Did not anticipate seeing another fellow lover of the logs! Excellent!

Chih-Chiun Chang - 6 years, 4 months ago

Superb :D classic method :)

Sandip Kumar - 6 years, 4 months ago

seriously amazing method...

priya kumari - 6 years, 2 months ago

eu fiz diferente na hora de resolver, de um jeito mais facil porem eu ia postar essa solução hehehe

Sswag SSwagf - 4 years, 8 months ago

How did you get to know that we need to take 4^m=k

Rohan Verma - 6 years, 4 months ago

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We do not know the value of "k" thence assign a variable any.

Daniel Ferreira - 6 years, 4 months ago

Lol xD you are a commerce student, aren't you?

Ananya Prakash - 6 years, 4 months ago
Max Harris
Sep 15, 2015

Using excel: Set A1 equal to 8 Set B1 equal to 1 Set C1 equal to =A1^B1 Set A2 equal to 4 Set C2 equal to =A2^B1

Open the Solver add in, set the target cell to C1, which will have a value of 27. Allow it to change cell B1. Hit solve.

Done.

Amer Sawan
Dec 27, 2015

8 = 2 × 2 × 2 8 = 2 \times 2 \times 2

8 m = ( 2 × 2 × 2 ) m = 27 8^{m} = ( 2 \times 2 \times 2 )^{m} = 27

2 m × 2 m × 2 m = 27 2^{m} \times 2^{m} \times 2^{m} = 27

if we took x = 2 m x=2^{m} then

3 × x = 3 × 9 3 \times x = 3 \times 9

x = 9 x=9 which means 2 m = 9 2^{m} =9

I like your solution... I really understand your easy solution

Zeeshan Sangri - 5 years ago

the best answer! thank you!

Naye Alvarez - 6 months, 3 weeks ago
Jonathus Narvato
Sep 3, 2015

Log 8^m = Log 27

m Log 8 = Log 27

m = Log 27 / Log 8

m = 1.585

Press your calculator to get 4 raised to the power of 1.585

4^1.585 = 9

answer 9

Eric Beck
Jul 19, 2016

It's a matter of reducing both sides to manipulate an answer here, without having to figure out the actual value of m. So, the problem offers us a base of 8 in one equation, and a base of 4 equalling the number that is the answer to this problem.

It is given that 8^M = 27, and again 4^M = ?

To reduce the base 8 to a similar base 4 in the other equation, knowledge and intuition would help guide in manipulating the 8 to be used as a 4; we have to take 8 to the power of a fraction that will output 4.

Knowing that 8 is 2 × 2 × 2, we can reduce this to 2^3. But, we also know that 2^3 still does not equal 4. Yes, we need to make the exponent 3 go under a numerator of 2 to manipulate further. Therefore, or in other words, the third root of 8 squared is 4.

8^(2/3) = 4 ==》 the base we want.

Awesome! So 4 can also be written, although not as friendly to the mind, or eyes, 8^(2/3) . Next, we must remember that if we reduce or manipulate in any way one side of an equation, the other side must have the same changing effect; The 8^(2/3 m) [ Remember we have that 'm' still in the exponent region] must also equal, symmetrically, 27^(2/3).

Alas, 8^(2/3 m) [OR as is starred above, 4^(m), and which is part of the second equation] = 27^(2/3) which reduces to a nice integer, 9.

Bryan Cusack
Oct 6, 2015

ln(27)/ln(8)=m, 4^m=9

Daniel Chen
Sep 4, 2015

I didn't even solve for m. 8 is 4 to the 3/2th power. Finding 27 to the 2/3th power gives 9.

Victor Stone
Mar 13, 2017

m log (8) = log (27) m = log (27)÷log (8) 4^(log (27)÷log (8)) is approximately 9

Greg Wroblewski
Feb 15, 2017

8 = 4 3 2 8=4^ \frac{3}{2}

4 3 m 2 = 27 4^ \frac{3m}{2}=27

4 m = 2 7 2 3 = 9 4^m=27^ \frac{2}{3}=9

8^m = 27 so, (2^3)^m = 3^3 Then, it can be (2^m)^3 = 3^3 Finally, 2^m = 3 We can find 4^m, which is equivalent with (2^2)^m or (2^m)^2 It means that (2^m)^2 = (3)^2 = 9

Gavin Hamilton
Dec 20, 2016

4^log8(27)

By trial and error 8^1. 8549= ~27

So: 4^1.8549 =~9 Of course I used my calculator 🙂

8^{ m } = 27 ... Applying log... m log8 = log 27-------- (eq(1)) ....nd let 4^{ m } = x and apply log to this eq... =>m log(4) = logx------(eq(2)) solving (eq(1)) nd (eq(2)) (which we can do in seconds)... we get l o g ( 27 ) l o g ( x ) \frac{log (27)}{log(x)} = 3 2 \frac{3}{2} so...

log(x) = log[(27)]^{ 2 3 \frac{2}{3} } = log(9) which gives us that x=9

Shaun Cairns
Jul 4, 2016

Use the BAQ method for logs: Base to the answer = the question so log(8) of 27 = 1.54.... So m = 1.54... Then 4^1.54 = 9

Badr AlWaili
Jun 21, 2016

m~1.5849624999 (by trying to guess the answer using the calculator) 4^(1.5849624999)~9

Not a good way of getting the answer, but it worked :)

Flavio Ripari
Jun 18, 2016

8^m = 27
<=> m = ln(27)/ln(8) = 1.58...

=> 4^m = 4^1.58... = 9

George Smith
Mar 30, 2016

4^log(8)27 = 9

Dominic Hunt
Mar 22, 2016

\log_8 27 = 1.58 so 4^1.58 = ~ 9

Sagar Tambe
Mar 9, 2016

8^m=27 8=(27)^(1/m) log(8)=(1/m)log(27) .9=(1/m)(1.43) (.9/.43)=1/m m=1/.63 m=1.6

4^m=9

Amed Lolo
Mar 1, 2016

4^m=p so m.ln(4)=ln(p),, 8=4^1.5,,27=9^1.5. 4^1.5m=9^1.5 ,,1.5m.ln4=1.5ln9. so m.ln4=ln9. Ln(p)=ln9 so,,,, p=4^m=9#####

Akash Kumar
Feb 23, 2016

First take log on both sides ... find m .... then put it in 4^m and get the answer...

Matthew Chin
Jan 29, 2016

Maybe this will be another solution: 8 m = 27 8 m = 3 3 m ln 8 = 3 ln 3 m = 3 l n 3 l n 8 m = 1.585 4 m = 9 { 8 }^{ m }=27\\ { 8 }^{ m }={ 3 }^{ { 3 } }\\ m\ln { 8 } =3\ln { 3 } \\ m=3*\frac { ln{ 3 } }{ ln{ 8 } } \\ m=1.585\\ { 4 }^{ m }=9

Kaleb Mason
Jan 25, 2016

8^m = 27

ln (8^m) = ln (27)

m * ln (8) = ln (27)

m = ln (27) / ln (8)

4^(ln (27) / ln (8)) = 9

Ramesh Jayaraman
Dec 25, 2015

8^m = 27 => m = log2 (3) => 4^m = 2^log2 (3^2) =9

Amit Dhunna
Nov 29, 2015

. 8^m = 27 .mlog(8)= log(27) . m=log(27)/log(8) . m=1.584962501 . 4^m=9

8^m = 27; 2^3m = 3^3 Therefore 2^m = 3, Then (2^m)^2 = 3^2: (2^2)^m = 9: ie 4^m = 9

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