Math Problem Statement

Evaluate the limit lim (n → ∞) (ln(2 + n) / (n + 1)).

Solution

To solve the given limit,

limnln(2+n)n+1,\lim_{n \to \infty} \frac{\ln(2 + n)}{n + 1},

let us proceed step by step.


Step 1: Analyze the behavior of the numerator and denominator

  • The numerator is ln(2+n)\ln(2 + n), which grows without bound as nn \to \infty, but much slower compared to linear or polynomial functions.
  • The denominator is n+1n + 1, which also grows without bound as nn \to \infty, but linearly.

Step 2: Apply asymptotic approximation

For large nn, 2+nn2 + n \approx n. Thus, ln(2+n)lnn\ln(2 + n) \approx \ln n. The expression simplifies to:

limnln(2+n)n+1limnlnnn+1.\lim_{n \to \infty} \frac{\ln(2 + n)}{n + 1} \approx \lim_{n \to \infty} \frac{\ln n}{n + 1}.


Step 3: Simplify further

Since n+1nn + 1 \approx n for large nn, the expression becomes:

limnlnnn.\lim_{n \to \infty} \frac{\ln n}{n}.


Step 4: Apply L’Hôpital’s Rule

The limit limnlnnn\lim_{n \to \infty} \frac{\ln n}{n} is an indeterminate form (\frac{\infty}{\infty}). Differentiating the numerator and denominator gives:

limnlnnn=limnddn(lnn)ddn(n)=limn1n1=limn1n.\lim_{n \to \infty} \frac{\ln n}{n} = \lim_{n \to \infty} \frac{\frac{d}{dn}(\ln n)}{\frac{d}{dn}(n)} = \lim_{n \to \infty} \frac{\frac{1}{n}}{1} = \lim_{n \to \infty} \frac{1}{n}.


Step 5: Evaluate the result

limn1n=0.\lim_{n \to \infty} \frac{1}{n} = 0.

Thus, the given limit evaluates to:

0.\boxed{0}.


Do you want a detailed explanation of any step? Here are 5 related questions you can explore:

  1. How does L’Hôpital’s Rule work in solving indeterminate forms?
  2. What are the growth rates of logarithmic versus polynomial functions?
  3. Can you derive the approximation ln(2+n)lnn\ln(2 + n) \approx \ln n for large nn?
  4. What are some other examples of limits involving logarithmic growth?
  5. Why does lnnn\frac{\ln n}{n} approach 00 as nn \to \infty?

Tip: When dealing with limits involving logarithms and polynomials, compare their growth rates to simplify the problem efficiently.

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Math Problem Analysis

Mathematical Concepts

Limits
Logarithms
Asymptotic Behavior
L'Hôpital's Rule

Formulas

lim (x → ∞) (ln(x)/x) = 0
L'Hôpital's Rule: lim (x → c) (f(x)/g(x)) = lim (x → c) (f'(x)/g'(x)) if the limit exists

Theorems

L'Hôpital's Rule
Asymptotic Approximations

Suitable Grade Level

Grades 11-12