Exponents #6

Algebra Level 2

( 4 9 ) x × ( 27 8 ) x 1 = log 4 log 8 \large { \left( \dfrac { 4 }{ 9 } \right) }^{ x }\times { \left( \dfrac { 27 }{ 8 } \right) }^{ x-1 }=\dfrac { \log { 4 } }{ \log { 8 } }

Find the value of x x satisfying the above equation.

1 0 2 1 2 -\frac { 1 }{ 2 }

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2 solutions

Akhil Bansal
Oct 8, 2015

( 4 9 ) x × ( 27 8 ) x 1 = log 4 log 8 \Rightarrow \left(\dfrac{4}{9}\right)^x \times \left(\dfrac{27}{8}\right)^{x-1} = \dfrac{\log 4}{\log 8} ( 2 3 ) 2 x × ( 3 2 ) 3 ( x 1 ) = log 2 2 log 2 3 \Rightarrow \left(\dfrac{2}{3}\right)^{2x} \times \left(\dfrac{3}{2}\right)^{3(x-1)} = \dfrac{\log 2^2}{\log 2^3} ( 2 3 ) 2 x × ( 2 3 ) 3 3 x = 2 3 log 2 log 2 \Rightarrow \left(\dfrac{2}{3}\right)^{2x} \times \left(\dfrac{2}{3}\right)^{3-3x} = \dfrac{2}{3} \dfrac{\log 2}{\log 2} ( 2 3 ) 2 x + 3 3 x = ( 2 3 ) 1 \Rightarrow \left(\dfrac{2}{3}\right)^{2x + 3 - 3x} = \left(\dfrac{2}{3}\right)^1 Bases are same, equating powers.
3 x = 1 x = 2 \Rightarrow 3 - x = 1 \Rightarrow \boxed{ x = 2 }

Ponhvoan Srey
Oct 8, 2015

( 4 9 ) x × ( 27 8 ) x 1 = log 4 log 8 ( 4 9 ) x × ( 27 8 ) x 1 = 2 3 ( 2 3 ) 2 x × ( 2 3 ) 3 s + 3 = 2 3 2 x 3 x + 3 = 1 x = 2 { \left( \frac { 4 }{ 9 } \right) }^{ x }\times { \left( \frac { 27 }{ 8 } \right) }^{ x-1 }=\frac { \log { 4 } }{ \log { 8 } } \\ \\ \quad { \left( \frac { 4 }{ 9 } \right) }^{ x }\times { \left( \frac { 27 }{ 8 } \right) }^{ x-1 }=\frac { 2 }{ 3 } \\ \\ { \left( \frac { 2 }{ 3 } \right) }^{ 2x }\times { \left( \frac { 2 }{ 3 } \right) }^{ -3s+3 }=\frac { 2 }{ 3 } \\ \\ \quad \quad \quad \quad \quad \Leftrightarrow 2x-3x+3=1\\ \\ \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \boxed { x=2 }

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