Determine the value of $\log_{3\sqrt{2}} \left( \frac{1}{18} \right)$.
Aptitude
Logarithm
Difficulty: Medium
Choose an option
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A$2$
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B$-2$
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C$\sqrt{2}$
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D$\sqrt{3}$
Answer
Correct Answer: $-2$
Explanation
Concept & Formula
To evaluate a logarithm with complex bases and fractional arguments, set the expression to a variable, convert to exponential form, and isolate the power.
$$ \log_a b = x \implies a^x = b $$
Step-by-Step Solution
* **Given:** Evaluate $\log_{3\sqrt{2}} \left( \frac{1}{18} \right)$.
* **Calculation:** Let the value be $x$. Convert to an exponential equation:
$$ (3\sqrt{2})^x = \frac{1}{18} $$
* Square the base $(3\sqrt{2})$ to see its relationship with $18$:
$$ (3\sqrt{2})^2 = 3^2 \cdot (\sqrt{2})^2 = 9 \cdot 2 = 18 $$
* Rewrite the right side of the equation ($\frac{1}{18}$) using negative exponents:
$$ \frac{1}{18} = 18^{-1} $$
* Substitute $18$ with $(3\sqrt{2})^2$:
$$ 18^{-1} = ((3\sqrt{2})^2)^{-1} = (3\sqrt{2})^{-2} $$
* Now, bring it back to our original equation:
$$ (3\sqrt{2})^x = (3\sqrt{2})^{-2} $$
* Equate the exponents:
$$ x = -2 $$
Exam Strategy & Shortcut
Observe the relationship between $3\sqrt{2}$ and $18$. Squaring $3$ gives $9$, and squaring $\sqrt{2}$ gives $2$. $9 \times 2 = 18$. Because the argument is $1/18$, the exponent must be negative. Answer is $-2$.
Common Pitfall
Getting intimidated by the $3\sqrt{2}$ base. Don't panic—square it first to see if it relates to the argument. Most aptitude questions are designed with perfect squares or cubes in mind.
Final Answer
**Therefore, the correct answer is -2.**