Chapter 11: Problem 63
Find the sum of the series. $$\sum_{n=0}^{\infty}(-1)^{n} \frac{X^{4 n}}{n !}$$
Short Answer
Expert verified
The sum of the series is \( e^{-X^4} \).
Step by step solution
01
Identify the Series Type
Observe that the given series is in the form \( \sum_{n=0}^{\infty} (-1)^n \frac{X^{4n}}{n!} \). This series resembles the Maclaurin series for the exponential function \( e^x \), specifically the series \( e^{-x} = \sum_{n=0}^{\infty} \frac{(-x)^n}{n!} \).
02
Substitute and Simplify
Substitute \( x = X^4 \) into the known series for \( e^{-x} \), which gives: \( e^{-X^4} = \sum_{n=0}^{\infty} \frac{(-X^4)^n}{n!} = \sum_{n=0}^{\infty} (-1)^n \frac{X^{4n}}{n!} \).
03
Match the Series
Notice that these two series are exactly the same, which confirms our substitution is correct. It matches the given series \( \sum_{n=0}^{\infty} (-1)^n \frac{X^{4n}}{n!} \).
04
Provide the Sum of the Series
Since the given series is equivalent to the series expansion of \( e^{-X^4} \), the sum of the series is \( e^{-X^4} \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Series Convergence
When we discuss series convergence, we're focusing on whether the sum of a series approaches a specific value as more terms are added. For a series to be convergent, the partial sums must approach a finite limit. In simpler terms, adding up the terms shouldn't result in a never-ending number; instead, it should settle to a particular number.
- A series like the one in our step by step solution, \( \sum_{n=0}^{\infty} (-1)^n \frac{X^{4n}}{n!} \), converges if its terms diminish swiftly enough.
- The convergence is often confirmed by comparing a series to a known convergent series.
Exponential Function
The exponential function, particularly in the context of calculus, is one of the most significant functions. It's often expressed as \( e^x \), where \( e \) is approximately 2.71828 and is known as Euler's number.
- The exponential function is central in describing continual growth or decay, such as in populations, radioactive decay, and even financial systems.
- In calculus, the series for \( e^x \) is represented as \( \sum_{n=0}^{\infty} \frac{x^n}{n!} \), which converges for all \( x \).
Substitution in Series
Substitution in series is a handy technique where we replace a variable in a known series expansion to derive a related series or solve a problem. Our exercise involved substituting \( x = X^4 \) into the exponential series \( e^{-x} = \sum_{n=0}^{\infty} \frac{(-x)^n}{n!} \).
- This substitution allowed us to match the given series with the known structure of the exponential function, transforming it into \( e^{-X^4} \).
- By recognizing this pattern, we simplify complex expressions and directly determine the sum of the series.
Infinite Series
An infinite series is an unending sum of elements from a sequence. In mathematical notation, this is represented by the sigma notation \( \sum_{n=0}^{\infty} a_n \), where \( a_n \) represents the sequence's terms.
- Calculating an infinite series means finding the sum between all terms starting from the initial term to infinity, a process effective when the series converges.
- A well-known example handled in coursework is the geometric series, which imparts foundational understanding of what it means for a series to converge.