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​f:N→N be a bounded function.Which of thefollowing statements is not true?f:\N\to\N\ \text{be a boun
Question

f:NN be a bounded function.Which of thefollowing statements is not true?f:\N\to\N\ \text{be a bounded function.Which of the}\\\text{following statements is not true?}​​

A.

lim supnf(n)N\limsup_{n \to \infty} f(n) \in \mathbb{N}​​

B.

lim infnf(n)N\liminf_{n \to \infty} f(n) \in \mathbb{N}​​

C.

lim infn(f(n)+n)N\liminf_{n \to \infty} \big(f(n) + n\big) \in \mathbb{N}​​

D.

lim supn(f(n)+n)N\limsup_{n \to \infty} \big(f(n) + n\big) \notin \mathbb{N}​​

Correct option is C

As f:NN is a bounded functionSo, limnf(n)=K(finite)So, limn(f(n)+n)=K+=lim infn(f(n)+n)=lim supn(f(n)+n)=So, lim infn(f(n)+n)NFor ex:-Let, f(n)=1n  limnf(n)=0 But,limn(1n+n)=N\text{As } f : \mathbb{N} \to \mathbb{N} \text{ is a bounded function} \\\text{So, } \lim_{n \to \infty} f(n) = K \quad (\text{finite}) \\\text{So, } \lim_{n \to \infty} \big(f(n) + n\big) = K + \infty = \infty \\\liminf_{n \to \infty} \big(f(n) + n\big) = \limsup_{n \to \infty} \big(f(n) + n\big) = \infty \\\text{So, } \liminf_{n \to \infty} \big(f(n) + n\big) \notin \mathbb{N}\\\textbf{For ex:-}\\ Let,\ f(n)=\frac{1}{n}\ \implies\lim_{n \to \infty} f(n) = 0\ But,\\\lim_{n \to \infty}(\frac{1}{n}+n)=\infty \notin\N​​

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