Chapter 5: Problem 34
Find the limits in Problems 1-60; not all limits require use of l'Hôpital's rule. $$ \lim _{x \rightarrow+\infty}\left(e^{x}-x^{n}\right), n \in \mathbf{N} $$
Short Answer
Expert verified
The limit is \( \infty \).
Step by step solution
01
Understand the Problem
We need to find the limit of the function \( f(x) = e^x - x^n \) as \( x \) approaches positive infinity. \( n \) is an element of the natural numbers \( \mathbb{N} \).
02
Identify Dominant Terms
As \( x \to +\infty \), we need to determine which part of the expression \( e^x - x^n \) grows faster. While \( e^x \) is an exponential function, \( x^n \) is a polynomial function. The exponential function \( e^x \) grows faster than any polynomial \( x^n \) as \( x \to +\infty \).
03
Simplify the Expression
Since \( e^x \) grows much faster than \( x^n \), for large \( x \), \( e^x \) will dominate the expression \( e^x - x^n \). Therefore, as \( x \to +\infty \), the term \( -x^n \) becomes negligible compared to \( e^x \).
04
Find the Limit
Given that \( e^x \) dominates \( x^n \) as \( x \to +\infty \), the expression \( e^x - x^n \) approaches \( e^x \) itself, which tends to infinity. Thus, the limit is \( \infty \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
l'Hôpital's rule
l'Hôpital's rule is a tool in calculus for finding the limit of indeterminate forms like \( \frac{0}{0} \) or \( \frac{\infty}{\infty} \). It's often used when direct substitution in a limit problem results in one of these indeterminate forms. The rule states that the limit of a quotient \( \frac{f(x)}{g(x)} \) as \( x \) approaches a certain value can be found by taking the derivative of the numerator and the denominator separately and then finding the limit of the resulting expression:\[\lim_{x \to c} \frac{f(x)}{g(x)} = \lim_{x \to c} \frac{f'(x)}{g'(x)}\]provided that the limit on the right exists.In our exercise, the limit becomes straightforward because the exponential function \( e^x \) grows much faster than the polynomial \( x^n \). This rapid growth avoids the creation of an indeterminate form, removing the need for l'Hôpital's rule. However, understanding this rule is crucial, as it offers a reliable way to tackle more complex limit problems.
exponential growth
Exponential growth describes a process where something increases rapidly by proportionally expanding at a constant rate over time. A classic example is the function \( e^x \), where \( e \) is the base of the natural logarithm, approximately equal to 2.71828. It's characterized by its ever-accelerating growth pattern as illustrated in the function \( e^x \).In the context of limits, this rapid growth is significant because it often points to \( e^x \) dominating other functions, such as polynomials, when \( x \) approaches infinity. For functions like \( e^x - x^n \), the exponential term \( e^x \) quickly overshadows the polynomial term \( x^n \). As a result, as \( x \to +\infty \), the limit is primarily governed by \( e^x \) itself, leading the expression to approach infinity.Exponential growth versus polynomial growth emphasizes the dramatic nature of functions based on \( e \). It's a core concept in calculus, finance, population dynamics, and numerous other fields.
polynomial functions
Polynomial functions comprise expressions of the form \( x^n \), with \( n \) being a non-negative integer. These functions are widely known for their predictable, steady growth, much slower than exponential functions. Polynomials can be as simple as linear (\( x \)) and quadratic (\( x^2 \)) or as complex as higher-degree forms (\( x^n \)).In limits, comparing the growth behavior is essential to identifying which part of a complex expression will dominate. For instance, with \( e^x - x^n \), the polynomial \( x^n \) grows at a fixed rate based on \( n \). Even though higher degrees mean faster growth, all polynomial terms eventually become negligible compared to \( e^x \) as \( x \to +\infty \).Understanding polynomial functions and their limitation in growth relative to exponential functions is vital when calculating limits. Specifically, it clarifies why \( e^x \) completely overtakes \( x^n \) as \( x \) becomes infinitely large.