Chapter 2: Problem 461
$$ \text { Find the polynomial function } f(x) \text { of least degree satisfying } \lim _{x \rightarrow 0}\left(1+\frac{f(x)}{x^{3}}\right)^{\frac{1}{x}}=e^{2} \text { . } $$
Short Answer
Expert verified
The polynomial function of least degree is \( f(x)=2x^2 \).
Step by step solution
01
Identify the limit rule to use
We immediately recognize the limit, as it resembles the definition of e, which states that \( \lim _{n \rightarrow \infty}\left(1+\frac{1}{n}\right)^{n}=e \). Here, x is going towards 0 instead of infinity, and \( \frac{1}{n} \) is replaced by \( \frac{f(x)}{x^{3}} \). Therefore, if we can make \( \frac{f(x)}{x^{3}} \) to be in the form of \( \frac{1}{x} \), then the limit would equal \( e^{2} \).
02
Find the form of \(f(x)\)
As we need \( \frac{f(x)}{x^{3}} \) to be in the form of \( \frac{1}{x} \), we can infer that \( f(x)=Ax^2 \), where A is the leading coefficient to be determined.
03
Determine the leading coefficient 'A'
The power to which e is raised to gives us value 2, and that directly relates to the value of A. Therefore, our leading coefficient A is 2.
04
State the polynomial function of least degree
Now we can determine \(f(x)\) based on our findings. Since \( f(x)=Ax^2 \) and A=2, our polynomial function of least degree is \( f(x)=2x^2 \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Understanding Limits
Limits are a key concept in calculus and serve as a foundational tool for analyzing functions as they approach a specific value. In this exercise, the limit considered is as \( x \) approaches 0. The expression resembles the definition of the mathematical constant \( e \), which is defined as \( \lim_{n \rightarrow \infty} \left(1 + \frac{1}{n} \right)^{n} = e \). This limit is crucial for understanding continuous growth processes.
In the given problem, the limit is structured as \( \lim_{x \rightarrow 0} \left(1 + \frac{f(x)}{x^3} \right)^{\frac{1}{x}} = e^2 \). Since this is analogous to the definition of \( e \), we adjust \( f(x) \) such that the argument inside the limit tends to resemble \( \frac{1}{x} \), allowing the whole expression to equate to \( e^2 \). Understanding how to manipulate functions to reach such states is a key part of working with limits.
In the given problem, the limit is structured as \( \lim_{x \rightarrow 0} \left(1 + \frac{f(x)}{x^3} \right)^{\frac{1}{x}} = e^2 \). Since this is analogous to the definition of \( e \), we adjust \( f(x) \) such that the argument inside the limit tends to resemble \( \frac{1}{x} \), allowing the whole expression to equate to \( e^2 \). Understanding how to manipulate functions to reach such states is a key part of working with limits.
Polynomial Degree and Structure
The degree of a polynomial is determined by the highest power of \( x \) in its expression. In this context, finding a polynomial of the least degree involves identifying the smallest power of \( x \) that satisfies the given conditions of the problem. Here, we infer that the polynomial function should be of degree 2 because we need \( \frac{f(x)}{x^3} \) in the form \( \frac{1}{x} \). Thus, if \( f(x) = Ax^2 \), then \( \frac{Ax^2}{x^3} = \frac{A}{x} \), matching the needed structure as \( x \to 0 \).
- Degree: The exponent of the highest power in the polynomial.
- Structure: Arrangement of terms based on their degree.
Connecting with Exponential Functions
Exponential functions are a class of functions where a constant base is raised to a variable exponent. They are crucial in describing growth processes, such as the spread of populations or financial models.
In the problem, the expression \( \left(1 + \frac{f(x)}{x^3} \right)^{\frac{1}{x}} \) takes on an exponential form where the power involves \( \frac{1}{x} \). The goal is to have this entire expression equate to \( e^2 \), linking back to the exponential nature of \( e \).
In the problem, the expression \( \left(1 + \frac{f(x)}{x^3} \right)^{\frac{1}{x}} \) takes on an exponential form where the power involves \( \frac{1}{x} \). The goal is to have this entire expression equate to \( e^2 \), linking back to the exponential nature of \( e \).
- Definition: Exponential functions have the form \( a^{x} \).
- Characteristic: Rapid growth or decay.
Role of the Leading Coefficient
The leading coefficient in a polynomial is the coefficient of the term with the highest degree. This value is critical as it influences the behavior of the polynomial, especially as \( x \) approaches infinity or other significant points.
In the solution of the problem, the leading coefficient \( A \) determines how \( f(x) = Ax^2 \) aligns with the given exponential condition, \( e^2 \). Since the problem specifies a \( 2 \) in the exponential \( e^2 \), \( A \) must be identified as \( 2 \) to satisfy the limit condition. This adjustment makes sure \( \left(1 + \frac{Ax^2}{x^3} \right)^{\frac{1}{x}} \) properly resolves to \( e^2 \).
In the solution of the problem, the leading coefficient \( A \) determines how \( f(x) = Ax^2 \) aligns with the given exponential condition, \( e^2 \). Since the problem specifies a \( 2 \) in the exponential \( e^2 \), \( A \) must be identified as \( 2 \) to satisfy the limit condition. This adjustment makes sure \( \left(1 + \frac{Ax^2}{x^3} \right)^{\frac{1}{x}} \) properly resolves to \( e^2 \).
- Importance: Dictates the growth behavior of polynomials.
- Determination: Directly linked to conditions given by limits or problem requirements.