Telescoping product of logs: Evaluate log₂3 × log₃2 × log₃4 × log₄3.
Aptitude
Logarithm
Difficulty: Easy
Choose an option
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A1
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B2
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C3
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D4
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E1/2
Answer
Correct Answer: 1
Explanation
Introduction / Context:Products of logarithms with swapped bases often telescope. The identity log_b a × log_a b = 1 is the key.
Given Data / Assumptions:
- All logs are valid (bases and arguments positive and not equal to 1).
Concept / Approach:Group the terms in pairs that invert bases and arguments: (log₂3 × log₃2) and (log₃4 × log₄3). Each pair equals 1.
Step-by-Step Solution:log₂3 × log₃2 = 1.log₃4 × log₄3 = 1.Product = 1 × 1 = 1.
Verification / Alternative check:Convert everything to natural logs: (ln 3/ln 2)(ln 2/ln 3)(ln 4/ln 3)(ln 3/ln 4) = 1.
Why Other Options Are Wrong:Any value ≠ 1 would contradict the base-inversion identity.
Common Pitfalls:Changing bases inconsistently or attempting unnecessary numeric approximations.
Final Answer:1