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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. For positive non-zero real variables $p$ and $q$, if 
    $\log (p^2 + q^2) = \log p + \log q + 2 \log 3$, 
    then, the value of $\frac{p^4+q^4}{p^2q^2}$ is

  2. 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

  3. A petrified wood fossil was discovered with 8 g of $^{14}C$. The decay of $^{14}C$ over time is given by: 

    $N_T = N_0 e^{-0.0001216T}$ 

    If the half-life of $^{14}C$ is 5700 years, and the fossil initially had 32 g of $^{14}C$, the age of the fossil in years is ______.

  4. For integers $a$, $b$ and $c$, what would be the minimum and maximum values respectively of $a + b + c$ if $\log |a| + \log |b| + \log |c| = 0$?
  5. The value of the expression $\frac{1}{1+\log_u vw} + \frac{1}{1+\log_v wu} + \frac{1}{1+\log_w uv}$ is
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