$(\log_5 5) (\log_4 9) (\log_3 2)$ is equal to
Aptitude
Logarithm
Difficulty: Medium
Choose an option
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A1
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B$\frac{3}{2}$
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C2
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D5
Answer
Correct Answer: 1
Explanation
### Concept & Formula
This problem involves simplifying individual logarithmic terms using the base-power property and then combining them using the reciprocal/chain rules of logarithms.
Base-Power Property:
$$ \log_{a^n}(b^n) = \log_a(b) $$
Reciprocal Property:
$$ \log_a(b) \cdot \log_b(a) = 1 $$
### Step-by-Step Solution
**Given expression:**
$(\log_5 5) \cdot (\log_4 9) \cdot (\log_3 2)$
Let's simplify each term one by one.
First term: $\log_5(5)$
The logarithm of any base to itself is always $1$.
$\log_5(5) = 1$
Second term: $\log_4(9)$
Recognize that both the base and the argument are perfect squares. Express them as powers:
$4 = 2^2$
$9 = 3^2$
Substitute these into the term:
$\log_{2^2}(3^2)$
Apply the base-power property ($\frac{2}{2} = 1$), reducing the term to:
$\log_2(3)$
Third term remains as is: $\log_3(2)$
Now, bring all the simplified terms back together into the original multiplication expression:
$1 \cdot (\log_2 3) \cdot (\log_3 2)$
$(\log_2 3) \cdot (\log_3 2)$
Use the reciprocal property of logarithms. Since the base of one is the argument of the other, their product is $1$:
$\log_2(3) \times \frac{1}{\log_2(3)} = 1$
### Exam Strategy & Shortcut
Whenever you see a logarithm where both the base and argument are raised to the same power, strip the powers immediately. $\log_4(9)$ is instantly just $\log_2(3)$. From there, you have a chain of $\log_2(3) \times \log_3(2)$. The bases and arguments criss-cross and cancel perfectly, leaving $1$. The $\log_5(5)$ is just a distractor that also equals $1$. $1 \times 1 = 1$.
### Common Pitfall
A common trap is trying to convert everything into base $10$ fractions right away without simplifying the perfect squares first. While $\frac{\log 9}{\log 4} \times \frac{\log 2}{\log 3}$ will eventually yield the right answer, it creates unnecessary and messy arithmetic steps that consume valuable exam time.
### Final Answer
**Therefore, the correct answer is 1.**