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Question

If a positive real $x$ satisfies the following equation
$$\log_2 x + \log_{\sqrt{2}} x = 48,$$
then the value of $x$ is _________________

The correct answer is
$2^{16}$

Solving the Logarithm Equation $\log_2 x + \log_{\sqrt{2}} x = 48$

Key Logarithm Properties Used

  • Change of base property: $\log_{b^k} a = \frac{1}{k} \log_b a$.
  • Combining like terms.

Step-by-Step Solution

  1. Simplify the second term: The base of the second logarithm is $\sqrt{2}$, which can be written as $2^{1/2}$. Using the property $\log_{b^k} a = \frac{1}{k} \log_b a$, we have:

    $\log_{\sqrt{2}} x = \log_{2^{1/2}} x = \frac{1}{1/2} \log_2 x = 2 \log_2 x$.

  2. Substitute back into the equation: Replace $\log_{\sqrt{2}} x$ with $2 \log_2 x$ in the original equation:

    $\log_2 x + 2 \log_2 x = 48$.

  3. Combine logarithmic terms: Add the terms involving $\log_2 x$:

    $3 \log_2 x = 48$.

  4. Isolate the logarithm: Divide both sides by 3:

    $\log_2 x = \frac{48}{3}$

    $\log_2 x = 16$.

  5. Solve for $x$: Convert the logarithmic equation to its exponential form. If $\log_b y = c$, then $y = b^c$.

    $x = 2^{16}$.

Final Answer

The value of $x$ that satisfies the equation $\log_2 x + \log_{\sqrt{2}} x = 48$ is $2^{16}$.

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Important Questions from Logarithms

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

  4. 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?

  5. 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 ______.

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