Chapter 9: Problem 2
Use the squeeze theorem to show that \(\lim _{n \rightarrow \infty} \frac{n !}{n^{n}}=0\).
Short Answer
Expert verified
Using the Squeeze Theorem, \( \lim_{n \to \infty} \frac{n!}{n^n} = 0 \).
Step by step solution
01
Understand the Squeeze Theorem
The Squeeze Theorem states that if \( f(n) \leq g(n) \leq h(n) \) for all \( n \) beyond some point, and \( \lim_{n \to \infty} f(n) = \lim_{n \to \infty} h(n) = L \), then \( \lim_{n \to \infty} g(n) = L \). To use this theorem, we need to find functions that "squeeze" \( \frac{n!}{n^n} \) as \( n \to \infty \).
02
Establish an Upper Bound
We aim to find a simple function that is always greater than or equal to \( \frac{n!}{n^n} \). Note that \( n! = 1 \times 2 \times 3 \times \ldots \times n \), which is less than \( n \times n \times n \times \ldots \times n = n^n \) since all factors from \( n! \) are less than or equal to \( n \). Thus, \( \frac{n!}{n^n} \leq 1 \).
03
Establish a Lower Bound that Converges to Zero
Consider \( \frac{1}{n^{n-1}} \) as a lower bound. As previously shown, \( n! < n \times n \times \ldots \times n = n^n \), so \( \frac{n!}{n^n} < \frac{n^n}{n^n} = 1 \). However, more importantly, each term \( k/n \) (where \( k \) is the factor in \( n! \)) is less than 1, so \[ \frac{n!}{n^n} < \left(\frac{n}{n}\right)^n = 1. \] Notice that the terms will decrease much faster than \( \frac{1}{n} \) as \( n \to \infty \).
04
Combine and Take the Limit
Now, since \( 0 \leq \frac{n!}{n^n} \leq 1 \) for all \( n \) beyond some point and since, for large \( n \), \( \frac{1}{n^{n-1}} \to 0 \) as \( n \to \infty \), we have by the Squeeze Theorem that \( \lim_{n \to \infty} \frac{n!}{n^n} = 0 \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Factorials
Factorials are a fundamental concept in mathematics, often denoted by an exclamation mark "!". When you see a number followed by a "!", it refers to the product of all positive integers up to that number. For example, 5! means 5 factorial, which is calculated as:\[5! = 5 \times 4 \times 3 \times 2 \times 1 = 120.\]Factorials appear frequently in permutations, combinations, and various mathematical expressions, signifying the total number of ways to arrange a set of items.
In this context, we use the factorial to understand ratios like \(\frac{n!}{n^n}\), where factorial growth is compared against exponential growth as n increases.
Because factorials grow rapidly, they are a key factor to consider when analyzing functions, especially where growth matters significantly.
In this context, we use the factorial to understand ratios like \(\frac{n!}{n^n}\), where factorial growth is compared against exponential growth as n increases.
Because factorials grow rapidly, they are a key factor to consider when analyzing functions, especially where growth matters significantly.
Limits
Limits are a cornerstone in calculus and analysis, used to understand the behavior of functions as the input values approach some point. In this case, we are interested in the limit of \(\frac{n!}{n^n}\) as \(n\) approaches infinity.The limit asks what value \(\frac{n!}{n^n}\) gets close to as \(n\) gets larger and larger. Essentially, we're trying to pinpoint the output of a function when the input is infinite, which is crucial in understanding the long-term behavior of mathematical sequences and series.
By employing the Squeeze Theorem, we can ascertain that the behavior of the sequence \(\frac{n!}{n^n}\) as \(n\) grows indefinitely approximates zero. Even though factorials increase rapidly, the denominator, being an exponential function \(n^n\), grows much faster, resulting in the whole fraction approaching zero.
By employing the Squeeze Theorem, we can ascertain that the behavior of the sequence \(\frac{n!}{n^n}\) as \(n\) grows indefinitely approximates zero. Even though factorials increase rapidly, the denominator, being an exponential function \(n^n\), grows much faster, resulting in the whole fraction approaching zero.
Asymptotic Behavior
Asymptotic behavior refers to how a function behaves as its inputs become very large. In mathematics, a function's asymptotic properties help us understand its growth trend in the long term.In applying the Squeeze Theorem, asymptotic analysis helps determine how \(\frac{n!}{n^n}\) compares to other sequences. Here,
- The exponential component \(n^n\) in the denominator far outpaces the factorial in the numerator as \(n\) increases.
- This difference in growth allows mathematicians to conjecture and eventually prove that \(\frac{n!}{n^n}\) converges to zero.