Let \(π(π) = π\) and \(π(π) = π^{(1+ sin \ π)}\) , where \(π\) is aβ¦
2015
LetΒ \(π(π) = π\) and \(π(π) = π^{(1+ sin \ π)}\) , whereΒ \(π\) is a positive integer. Which of the following statements is/are correct?
I.Β π(π) = π(π(π))
II.Β π(π) = β¦(π(π))
- A.
Only I
- B.
Only II
- C.
Both I and II
- D.
Neither I nor II
Attempted by 270 students.
Show answer & explanation
Correct answer: D
Key idea: sin n oscillates between -1 and 1, and for infinitely many integers n it can be made arbitrarily close to -1 or to 1.
If sin n is very close to -1 (along some subsequence), then 1+sin n is near 0, so g(n)=n^{1+sin n}=n^{Ξ΅} with Ξ΅β0. In that case g(n)=o(n) and f(n)/g(n)ββ, so f(n) is not O(g(n)).
If sin n is very close to 1 (along another subsequence), then 1+sin n is near 2, so g(n)βn^2 and f(n)/g(n)β1/nβ0, so f(n) is not β¦(g(n)).
Conclusion: Because g(n) can be arbitrarily much smaller than n for some n and arbitrarily much larger for other n, neither f(n)=O(g(n)) nor f(n)=β¦(g(n)) holds. Therefore neither statement is correct.
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