Correct : c
Explanation:
Let us simplify the given logarithmic equation step-by-step using standard logarithm rules.
1. Apply Logarithmic Properties:
The given equation is:
ln((x + y) / 2) = 1/2 [ln(x) + ln(y)]
Using the log addition rule, ln(x) + ln(y) = ln(xy):
ln((x + y) / 2) = 1/2 ln(xy)
Using the power rule, b · ln(a) = ln(ab):
ln((x + y) / 2) = ln((xy)1/2)
2. Remove the Natural Logarithm from Both Sides:
(x + y) / 2 = √(xy)
x + y = 2√(xy)
3. Square Both Sides to Eliminate the Radical:
(x + y)2 = (2√(xy))2
x2 + 2xy + y2 = 4xy
Bring 4xy to the left side:
x2 - 2xy + y2 = 0
(x - y)2 = 0
x - y = 0 → x = y
4. Evaluate the Target Expression:
Since x = y, we substitute y for x (or vice versa) in the expression x/y + y/x:
x/y + y/x = y/y + y/y = 1 + 1 = 2
5. Conclusion:
The value of the expression is exactly 2, making option (c) the correct choice.
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