Solve the logarithmic equation:

Algebra Level 2

Solve the logarithmic equation: log x ( 2 ( 1 x ) ) log 1 x ( 2 x ) = 0 \log_x (2(1-x))- \log_{1-x} (2x) = 0


The answer is 0.5.

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2 solutions

Hugh Sir
Nov 21, 2018

log x ( 2 ( 1 x ) ) = log 1 x ( 2 x ) \log_{x}(2(1-x)) = \log_{1-x} (2x)

log ( 2 ( 1 x ) ) log x = log ( 2 x ) log ( 1 x ) \dfrac{\log (2(1-x))}{\log x} = \dfrac{\log (2x)}{\log (1-x)}

( log 2 + log ( 1 x ) ) ( log ( 1 x ) ) = ( log 2 + log x ) ( log x ) (\log 2+\log (1-x))(\log (1-x)) = (\log 2+\log x)(\log x)

log 2 ( 1 x ) log 2 x + ( log 2 ) ( log ( 1 x ) log x ) = 0 \log^{2} (1-x) - \log^{2} x + (\log 2)(\log (1-x)-\log x) = 0

( log ( 1 x ) log x ) ( log ( 1 x ) + log x + log 2 ) = 0 (\log (1-x)-\log x)(\log (1-x)+\log x+\log 2) = 0

  • If log ( 1 x ) log x = 0 \log (1-x)-\log x = 0 , then 1 x = x x = 0.5 1-x = x \implies \boxed{x = 0.5} .
  • If log ( 1 x ) + log x + log 2 = 0 \log (1-x)+\log x+\log 2 = 0 , then 2 x 2 2 x + 1 = 0 2x^{2}-2x+1 = 0 . This equation has no real root.

Therefore, the answer is x = 0.5 x = 0.5 .

Chew-Seong Cheong
Nov 21, 2018

log x ( 2 ( 1 x ) ) log 1 x ( 2 x ) = 0 log x ( 2 ( 1 x ) ) = log 1 x ( 2 x ) \begin{aligned} \log_x (2(1-x)) - \log_{1-x}(2x) & = 0 \\ \implies \log_{\color{#D61F06}x} (2{\color{#3D99F6}(1-x)}) & = \log_{\color{#3D99F6}1-x}(2{\color{#D61F06}x}) \end{aligned}

Equating the logarithm bases and the operants, we have x = 1 x x=1-x x = 1 2 = 0.5 \implies x = \dfrac 12 = \boxed{0.5} .

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