LOGARITHM Problem For Fun

Level 2

Given that α > 1 \alpha>1 , β > 0 \beta>0 , Is there any real number solutions for l o g α X log_\alpha X for the expression below. log α X l o g α ( X β ) = 1 \log_\alpha X -log_\alpha ( X -\beta) =-1

Yes for all values of alpha and beta Yes for some, none for others None

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3 solutions

Jordan Cahn
Oct 23, 2018

Assume that log α X \log_\alpha X has a real solution. Using logarithm identities: log α X log α ( X β ) = 1 log α ( X X β ) = 1 X X β = α 1 X X β = 1 α \begin{aligned} \log_\alpha X - \log_\alpha (X-\beta) &= -1 \\ \log_\alpha \left(\frac{X}{X-\beta}\right) &= -1 \\ \frac{X}{X-\beta} &= \alpha^{-1} \\ \frac{X}{X-\beta} &= \frac{1}{\alpha} \end{aligned} Since β > 0 \beta>0 , X > X β X>X-\beta and, therefore, X X β > 1 \frac{X}{X-\beta}>1 . But α > 1 \alpha>1 , so 1 α < 1 \frac{1}{\alpha}<1 , a contradiction.

Thus there are no real solutions, regardless of the values of α \alpha and β \beta . The answer is None .

Parth Sankhe
Oct 22, 2018

If the given equation is true, then ( x B ) > x (x-B)>x , for A>1.

That would mean B<0, which contradicts the given statement.

Tan Peng
Oct 22, 2018

We can Simplify the expression above to X= - β \beta /( α 1 ) \alpha -1) Since alpha and beta are positive X must be negative .Let l o g α X = n log_\alpha X = n .Then there will be no real number that satisfy n because no positive number to the power of a real number is a negative.

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