Interesting Exponents

Algebra Level 1

If 8 m = 27 8^m=27 , what is the value of 4 m 4^m ?


The answer is 9.

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9 solutions

A K
Apr 30, 2014

This can be written as:

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

Therefore:

( 2 2 m ) 3 2 = 27 { ({ 2 }^{ 2m }) }^{ \frac { 3 }{ 2 } } = 27

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

I went by a slightly different method.

I first took cube root on both sides, giving me 2^m=3

then I squared both sides, which gives 2^2m=9 or 4^m=9!!!

easy!!

Krishna Ramesh - 7 years, 1 month ago

woahh!!..i did this w/out solution ... analyzing the problem when you dont know it can improve your brain...

Cj Lefron Juntilla - 6 years, 9 months ago

Nice solution, this is the same as how I did it but another method is 4^ IN(3)/(In 2)

Mardokay Mosazghi - 7 years, 1 month ago

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did it same way.

A Former Brilliant Member - 4 years, 10 months ago

I did it same way.

Arghyanil Dey - 7 years ago
Rakshit Pandey
Jul 17, 2014

8 m = 27 8^m=27
( 2 3 ) m = 27 \Rightarrow(2^3)^m=27
( 2 m ) 3 = 3 3 \Rightarrow(2^m)^3=3^3
2 m = 3 \Rightarrow 2^m=3
( 2 m ) 2 = 3 2 \Rightarrow(2^m)^2=3^2 (Squaring both sides)
( 2 2 ) m = 9 \Rightarrow(2^2)^m=9
4 m = 9 \Rightarrow 4^m=9



N Solomon
Jul 12, 2014

8 m = ( 4 × 2 ) m = 4 m × 2 m 8^{m} = (4 \times 2)^{m} = 4^{m} \times 2^{m}

4 m × 2 m = 27 4^{m} \times 2^{m} = 27

So, 4 m = 27 2 m 4^{m} = \frac{27}{2^{m}} .

If: m = l o g 8 27 m = log_8 27

then: 4 m = 27 2 l o g 8 27 = 27 3 = 9 4^{m} = \frac{27}{2^{log_8 27}} = \frac{27}{3} = \boxed{9} .

Alternatively: 4 m = 4 l o g 8 27 = 9 4^{m} = 4^{log_8 27} = \boxed{9}

Andi Setiawan
Sep 8, 2015

8 m = 27 8^{m}=27 ----> 2 3 m = 3 3 2^{3m} = 3^3

3 m . l n 2 = 3. l n 3 3m.ln 2 = 3.ln 3

m . l n 2 = l n 3 m.ln 2 = ln 3

2 m = 3 2^m = 3

4 m = 2 m . 2 m = 3 x 3 = 9 \boxed{4^m = 2^m.2^m = 3x3 = 9}

Syeda Hussain
Jul 6, 2015

2^3m=3^3 2^2m=3^2 so, 9

Aneesh S.
Jun 30, 2015

To find the value of m m , we must take the logarithm in base 8 of each side and work from there onwards:

log 8 8 m = log 8 27 \log _{ 8 }{ { 8 }^{ m } = \log _{ 8 }{ 27 } }

Due to the Power Property of logarithms ( log b m n = n ( log b m ) \log _{ b }{ { m }^{ n } } =n(\log _{ b }{ m } ) ) we are able to simplify the left side of the equation:

log 8 8 m = m ( log 8 8 ) = m ( 1 ) = m \log _{ 8 }{ { 8 }^{ m } } =m(\log _{ 8 }{ 8 } )=m(1)=m

For now, we will express the right side as simply l o g 8 27 log _{ 8 }{ 27 } .

After simplifying this equation, we know that m = log 8 27 m= \log_{8}{27} .

The question asks what the value of 4 m { 4 }^{ m } is. To find it, we have to plug our value of m m back into this expression:

4 ( log 8 27 ) { 4 }^{ (\log _{ 8 }{ 27 } ) } of which the answer is 9 \boxed{9}

Daniel Ferreira
Feb 28, 2015

8 m = 27 log 8 27 = m log 2 3 3 3 = m 1 3 3 log 2 3 = m log 2 3 = m 2 m = 3 ( 2 m ) 2 = ( 3 ) 2 2 2 m = 9 ( 2 2 ) m = 9 4 m = 9 8^m = 27 \\\\ \log_8 27 = m \\\\ \log_{2^3} 3^3 = m \\\\ \frac{1}{3} \cdot 3 \cdot \log_2 3 = m \\\\ \log_2 3 = m \\\\ 2^m = 3 \\\\ (2^m)^2 = (3)^2 \\\\ 2^{2m} = 9 \\\\ (2^2)^m = 9 \\\\ \boxed{4^m = 9}

Hassan Raza
Aug 1, 2014

Given\quad that\\ \qquad \qquad { 8 }^{ m }={ 27 }\\ Step\quad I\\ \qquad Take\quad cube\quad root\quad on\quad both\quad sides.\\ \qquad \quad \quad { { (8 }^{ m }) }^{ \frac { 1 }{ 3 } }={ 27 }^{ \frac { 1 }{ 3 } }\quad =>\quad { { (2 }^{ 3m }) }^{ \frac { 1 }{ 3 } }={ ({ 3 }^{ 3 }) }^{ \frac { 1 }{ 3 } }\\ or\qquad \boxed { { 2 }^{ m }={ 3 } } \\ Step\quad II\\ \qquad Now\quad take\quad squre\quad on\quad both\quad sides\\ \qquad { { ( }2^{ m }) }^{ 2 }={ 3 }^{ 2 }\\ we\quad get\quad \boxed { { 4 }^{ m }=9 } \\

Bill Bell
Jul 23, 2014

8 m = ( 2 3 ) m = ( 2 m ) 3 = 27 2 m = 3 ( 2 m ) 2 = ( 2 2 ) m = 4 m = 9 { 8 }^{ m }={ ({ 2 }^{ 3 }) }^{ m }={ ({ 2 }^{ m }) }^{ 3 }=27\quad \Rightarrow \quad { 2 }^{ m }=3\quad \Rightarrow \quad { ({ 2 }^{ m }) }^{ 2 }={ ({ 2 }^{ 2 }) }^{ m }={ 4 }^{ m }=9

A fun one!

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