Math Problem Statement

lim ntoinf ln(n)/sqrtn

Solution

We aim to evaluate the limit:

limnln(n)n\lim_{n \to \infty} \frac{\ln(n)}{\sqrt{n}}

Step-by-step Solution:

  1. Examine the growth rates of the numerator and denominator:

    • The numerator ln(n)\ln(n) grows much slower than any power of nn.
    • The denominator n\sqrt{n} grows much faster than ln(n)\ln(n) because n\sqrt{n} is a power function of nn.
  2. Apply intuition:

    • Since the denominator n\sqrt{n} grows much faster than the numerator ln(n)\ln(n), the fraction ln(n)n\frac{\ln(n)}{\sqrt{n}} should approach 0 as nn \to \infty.
  3. Formal approach using L'Hopital's Rule:

    • This limit is of the indeterminate form \frac{\infty}{\infty}. L'Hopital's Rule allows us to differentiate the numerator and denominator: [ \lim_{n \to \infty} \frac{\ln(n)}{\sqrt{n}} = \lim_{n \to \infty} \frac{\frac{d}{dn}[\ln(n)]}{\frac{d}{dn}[\sqrt{n}]}. ]
    • Compute the derivatives: [ \frac{d}{dn}[\ln(n)] = \frac{1}{n}, \quad \frac{d}{dn}[\sqrt{n}] = \frac{1}{2\sqrt{n}}. ]
    • Substituting back: limnln(n)n=limn1n12n=limn2nn.\lim_{n \to \infty} \frac{\ln(n)}{\sqrt{n}} = \lim_{n \to \infty} \frac{\frac{1}{n}}{\frac{1}{2\sqrt{n}}} = \lim_{n \to \infty} \frac{2\sqrt{n}}{n}.
    • Simplify the new expression: 2nn=2n.\frac{2\sqrt{n}}{n} = \frac{2}{\sqrt{n}}.
  4. Evaluate the simplified limit:

    • As nn \to \infty, n\sqrt{n} \to \infty, so: limn2n=0.\lim_{n \to \infty} \frac{2}{\sqrt{n}} = 0.

Final Answer:

limnln(n)n=0.\lim_{n \to \infty} \frac{\ln(n)}{\sqrt{n}} = 0.


Would you like further clarification on any part of this solution?

Related Questions:

  1. How does the growth rate of logarithmic functions compare to polynomial functions?
  2. What is the general application of L'Hopital's Rule in limits?
  3. Why does ln(n)\ln(n) grow slower than n\sqrt{n}?
  4. How would this change if the denominator were ln(n)k\ln(n)^k instead of n\sqrt{n}?
  5. Can we evaluate the same limit using series approximations?

Tip:

When dealing with limits involving growth rates, always compare the relative growth speeds of the numerator and denominator.

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Math Problem Analysis

Mathematical Concepts

Limits
Logarithmic Functions
Power Functions
Growth Rates
L'Hopital's Rule

Formulas

Limit definition: lim_{n→∞} f(n)/g(n)
L'Hopital's Rule: lim_{x→c} f(x)/g(x) = lim_{x→c} f'(x)/g'(x) for indeterminate forms
Derivative of ln(n): d/dn[ln(n)] = 1/n
Derivative of sqrt(n): d/dn[sqrt(n)] = 1/(2sqrt(n))

Theorems

L'Hopital's Rule

Suitable Grade Level

Grades 11-12 or Undergraduate Calculus