- A
- B
- C
- D
View written solutionFree
Correct answer: A
Step-by-step Solution:
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Analyze the given functions and relations. We are given , where
f(x)is a twice differentiable positive function on . The functionf(x)satisfies the functional equationf(x + 1) = xf(x). -
Establish a relationship for
g(x)using the functional equation. Take the natural logarithm of both sides of the functional equation forf(x): Using the properties of logarithms, we can write: From the definition , we have . Substituting this into the equation above gives: -
Differentiate the relation for
g(x)to find a relation for its derivatives. Differentiate the equation with respect tox: Applying the chain rule, we get: Now, differentiate this equation again with respect tox: This gives us a recurrence relation forg''(x): -
Evaluate the expression
g''(N + 1/2) - g''(1/2)using the recurrence relation. The expression can be written as a telescoping sum: Let's verify this sum: Fork=1:g''(3/2) - g''(1/2)Fork=2:g''(5/2) - g''(3/2)... Fork=N:g''(N+1/2) - g''(N-1/2)Summing these terms, all intermediate terms cancel out, leavingg''(N+1/2) - g''(1/2). -
Apply the recurrence relation to the terms in the sum. Our recurrence relation is . For each term in the sum, let
x = k - 1/2. Thenx + 1 = k - 1/2 + 1 = k + 1/2. Substitutingx = k - 1/2into the recurrence relation gives: -
Calculate the final sum. Now we can substitute this back into our telescoping sum expression: Expanding the sum:
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Compare with the given options. The result matches option A.
Final Answer is option A.
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