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Unit 1 · Discrete Structures and Optimisation Paper 2 CS · June 2024 (Cancelled Exam)

If f(n) = 5f(n/2) + 3 and f(1) = 7 is a recurrence relation, where k is a positive integer, then f(2ᵏ) =

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Correct answer: A. 5ᵏ(31/4) − 3/4

Explanation

With aₖ = f(2ᵏ): aₖ = 5aₖ₋₁ + 3, a₀ = 7. The solution is aₖ = 5ᵏ·7 + 3(5ᵏ − 1)/4 = 5ᵏ(31/4) − 3/4.

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