Simplify the logarithmic expression: log(75/16) − 2·log(5/9) + log(32/343). Express the result as a single logarithm and identify its exact simplified form.

Difficulty: Medium

Correct Answer: log(486/343)

Explanation:


Introduction / Context:
This problem tests manipulation of logarithms using the product, quotient, and power rules. We combine all terms into a single logarithm and then simplify the numeric argument exactly.


Given Data / Assumptions:

  • Expression: log(75/16) − 2·log(5/9) + log(32/343)
  • All logs share the same base.


Concept / Approach:
Use log A − 2·log B + log C = log( A·C / B^2 ). Evaluate the fraction precisely and reduce to lowest terms.


Step-by-Step Solution:

Start with: log(75/16) − 2·log(5/9) + log(32/343)= log( (75/16) * (32/343) / ( (5/9)^2 ) )Compute inside: (75/16) * (32/343) = (7532)/(16343) = (752)/343 = 150/343Divide by (25/81): (150/343) / (25/81) = (150/343) * (81/25) = (681)/343 = 486/343Hence the expression equals log(486/343)


Verification / Alternative check:
Prime-factor view: 486 = 2·3^5 and 343 = 7^3, so the exact simplest form is log( (2·3^5) / 7^3 ). No further cancellation exists, confirming the simplified form.


Why Other Options Are Wrong:
Values like log 2, 2 log 2, log 3, or log 5 would require the fraction to simplify to 2, 4, 3, or 5 respectively, which it does not; 486/343 ≈ 1.417 is distinct.


Common Pitfalls:
Missing the square on the middle term (because of the coefficient 2) or dropping factors during fraction reduction can lead to incorrect constants like log 2 or log 3. Carefully track numerators and denominators.


Final Answer:
log(486/343)

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