Chapter 11: Problem 65
Write the sum using sigma notation. $$1+x+x^{2}+x^{3}+\cdots+x^{100}$$
Short Answer
Expert verified
The sum is written as \( \sum_{n=0}^{100} x^n \).
Step by step solution
01
Identify the Pattern
Look at the sum: \(1, x, x^2, x^3, \ldots, x^{100}\). Notice that each term is a power of \(x\), starting from \(x^0\) and ending at \(x^{100}\). This sequence suggests a pattern of powers of \(x\).
02
Define the General Term
From the pattern, we can see that the general term of the sequence is \(x^n\), where \(n\) starts from \(0\) and goes up to \(100\). Thus, the general term that we want to sum is \(x^n\).
03
Write the Sum using Sigma Notation
Sigma notation is used to write sums compactly. The general form is \( \sum_{n=a}^{b} \, f(n) \), where \(a\) and \(b\) are the limits of the sum and \(f(n)\) is the general term. In this case, the sum becomes \( \sum_{n=0}^{100} x^n \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Power Series
Power series are expressions of the form \( a_0 + a_1x + a_2x^2 + a_3x^3 + \cdots \). They allow us to represent functions as infinite sums through a sequence of coefficients \(a_n\). Power series are a powerful tool in mathematics because they can represent many important functions. For example, the exponential function \( e^x \) is represented by the power series \( 1 + x + \frac{x^2}{2!} + \frac{x^3}{3!} + \cdots \).
- Each term in the series is a multiple of a power of \(x\).
- The number of terms in a power series can be finite or infinite.
- The general form of a power series can be written as \( \sum_{n=0}^{\infty} a_n x^n \).
Geometric Series
A geometric series is a specific type of series where each term is a constant multiple of the previous one. If you look at the series \(1 + x + x^2 + x^3 + \ldots + x^{100}\), it is a geometric series because each term is obtained by multiplying the previous term by \(x\). The series ends with the term \(x^{100}\), making it a finite geometric series.
- In a geometric series, the ratio between successive terms is constant, often referred to as the common ratio.
- The formula for the sum of a finite geometric series is \( S_n = a \frac{1-r^n}{1-r} \), where \(a\) is the first term, \(r\) is the common ratio, and \(n\) is the number of terms.
- For an infinite geometric series with \(|r| < 1\), the sum is \( \frac{a}{1-r} \).
Summation Notation
Summation notation, often represented using the Greek letter sigma (\( \Sigma \)), is a method to denote the sum of a sequence of terms. Instead of writing out each term individually, summation notation provides a compact way to express series and sums using a clear mathematical format.
- The typical sigma notation form is \( \sum_{n=a}^{b} f(n) \), where \(n\) is the index of summation, \(a\) starts the sum, \(b\) ends it, and \(f(n)\) is the function defining the terms.
- It allows mathematicians to convey large sums succinctly, such as \( \sum_{n=0}^{100} x^n \) for the series \(1 + x + x^2 + \cdots + x^{100}\).
- This notation is versatile and can represent both finite and infinite sums depending on the context.