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Question

Real numbers $y$, $p$, and $n$ (all greater than 1) satisfy
$$(\log_{p^{1/n}} y)(\log_{y^{1/n}} p) = 16,$$
where the logarithms are taken to the bases $p^{1/n}$ and $y^{1/n}$.
The value of $n$ is ________

The correct answer is
4

Solving the Logarithm Equation

We are given the equation involving real numbers $y, p, n$ (all greater than 1):

$(\log_{p^{1/n}} y)(\log_{y^{1/n}} p) = 16$

We need to find the value of $n$. Let's simplify the logarithmic terms using logarithm properties.

Logarithm Property Application

Recall the logarithm property: $\log_{a^k} b = \frac{1}{k} \log_a b$. Applying this to our terms:

  • The first term: $\log_{p^{1/n}} y = \frac{1}{1/n} \log_p y = n \log_p y$
  • The second term: $\log_{y^{1/n}} p = \frac{1}{1/n} \log_y p = n \log_y p$

Substitute these simplified terms back into the original equation:

$(n \log_p y)(n \log_y p) = 16$ $n^2 (\log_p y)(\log_y p) = 16$

Simplifying to Find n

Now, use the change of base property for logarithms: $\log_a b = \frac{1}{\log_b a}$. This means $\log_y p = \frac{1}{\log_p y}$. Substitute this into the equation:

$n^2 (\log_p y) \left(\frac{1}{\log_p y}\right) = 16$

The term $(\log_p y)$ cancels out (since $y > 1$, $\log_p y$ is non-zero):

$n^2 = 16$

To find $n$, we take the square root of both sides:

$n = \pm \sqrt{16}$ $n = \pm 4$

The problem states that $n > 1$. Therefore, we choose the positive value.

$n = 4$

Final Answer Determination

The value of $n$ that satisfies the given conditions is 4.

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Important Questions from Logarithms

  1. Consider two distinct positive real numbers $m, n$, with $m > n$.

    Let $x = n^{\log_{10}(m)}$ and $y = m^{\log_{10}(n)}$. The relation between $x$ and $y$ is _______.

  2. If $\log_x (5/7) = -1/3$, then the value of $x$ is
  3. A value of x that satisfies the equation $ \log x + \log (x - 7) = \log (x + 11) + \log 2 $ is
  4. For a real number $x > 1$, 
    $\frac{1}{\log_2 x} + \frac{1}{\log_3 x} + \frac{1}{\log_4 x} = 1$ 
    The value of $x$ is

  5. Let $a = 30!$, $b = 50!$, and $c = 100!$. Consider the following numbers: 

    $log_a c$,           $log_c a$,           $log_b a$,             $log_a b$ 

    Which one of the following inequalities is CORRECT?

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