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Question

If Log (P) = (1/2)Log (Q) = (1/3) Log (R), then which of the following options is TRUE?

The correct answer is
$Q^2 = PR$

Logarithmic Relationship Analysis

The problem asks to identify the true relationship among P, Q, and R given the logarithmic equality:

$ \log(P) = \frac{1}{2}\log(Q) = \frac{1}{3}\log(R) $

Deriving Variable Relationships

We use the properties of logarithms to establish connections between the variables. Let the common value of the expressions be $k$. This means:

  • $\log(P) = k \implies P = b^k$ (where $b$ is the base of the logarithm)
  • $\frac{1}{2}\log(Q) = k \implies \log(Q) = 2k \implies Q = b^{2k}$
  • $\frac{1}{3}\log(R) = k \implies \log(R) = 3k \implies R = b^{3k}$

Alternatively, using logarithm properties directly:

  • From $\log(P) = \frac{1}{2}\log(Q)$, we get $2\log(P) = \log(Q)$, which implies $\log(P^2) = \log(Q)$, so $P^2 = Q$.
  • From $\log(P) = \frac{1}{3}\log(R)$, we get $3\log(P) = \log(R)$, which implies $\log(P^3) = \log(R)$, so $P^3 = R$.

We now have $Q = P^2$ and $R = P^3$. We will use these to check the given options.

Evaluating Options

Substitute $Q = P^2$ and $R = P^3$ into each option:

  1. Option 1: $P^2 = Q^3R^2$
    $ P^2 = (P^2)^3 (P^3)^2 $
    $ P^2 = P^6 \cdot P^6 $
    $ P^2 = P^{12} $

    This is not generally true.

  2. Option 2: $Q^2 = PR$
    $ (P^2)^2 = P \cdot (P^3) $
    $ P^4 = P^4 $

    This statement is TRUE.

  3. Option 3: $Q^2 = R^3P$
    $ (P^2)^2 = (P^3)^3 \cdot P $
    $ P^4 = P^9 \cdot P $
    $ P^4 = P^{10} $

    This is not generally true.

  4. Option 4: $R = P^2Q^2$
    $ P^3 = P^2 \cdot (P^2)^2 $
    $ P^3 = P^2 \cdot P^4 $
    $ P^3 = P^6 $

    This is not generally true.

Conclusion

The relationship $Q^2 = PR$ holds true based on the initial logarithmic conditions.

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Important Questions from Logarithms

  1. 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 ________
  2. 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 _______.

  3. If $\log_x (5/7) = -1/3$, then the value of $x$ is
  4. A value of x that satisfies the equation $ \log x + \log (x - 7) = \log (x + 11) + \log 2 $ is
  5. 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

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