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If n≥2,n\ge 2,n≥2, then the value of 1+12+13+...+1n1+\frac 12+\frac 13+...+\frac1n1+21​+31​+...+n1​ is​
Question

If n2,n\ge 2, then the value of 1+12+13+...+1n1+\frac 12+\frac 13+...+\frac1n is​

A.

2n3\leq \sqrt{2n - 3} \\​​

B.

>2n> 2n \\​​

C.

>2nn+1> \frac{2n}{n + 1} \\​​

D.

<2nn+1< \frac{2n}{n + 1} \\​​

Correct option is C

Solution:

H(n)=1+12+13++1n,where n2H(n)>2nn+1The harmonic series grows slowly but satisfies the inequality:H(n)>2nn+1 for all n2Example: For n=2,H(2)=1+12=322nn+1=4332>43, so the inequality holds.This pattern continues for larger values of n.H(n) = 1 + \frac{1}{2} + \frac{1}{3} + \cdots + \frac{1}{n}, \quad \text{where } n \geq 2\\[10pt]H(n) > \frac{2n}{n + 1}\\[10pt]\begin{aligned}&\text{The harmonic series grows slowly but satisfies the inequality:} \\&H(n) > \frac{2n}{n + 1} \text{ for all } n \geq 2 \\&\text{Example: For } n = 2, \\&H(2) = 1 + \frac{1}{2} = \frac{3}{2} \\&\frac{2n}{n + 1} = \frac{4}{3} \\&\frac{3}{2} > \frac{4}{3}, \text{ so the inequality holds.} \\&\text{This pattern continues for larger values of } n.\end{aligned}​​

​​Final Answer:
(c) >2nn+1\boxed{\text{(c) } > \frac{2n}{n + 1}}​​


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