Chapter 10: Problem 3
Find the first four terms of the binomial series for the functions. \begin{equation} (1-x)^{-3} \end{equation}
Short Answer
Expert verified
The first four terms are: 1, -3x, 6x^2, -10x^3.
Step by step solution
01
Identify the Binomial Series Formula
The binomial series \[(1-x)^n = \sum_{k=0}^{\infty} \binom{n}{k} (-x)^k\] is used when \(|x| < 1\) and \(n\) is any real number.
02
Substitute and Calculate Binomial Coefficients
For the function \((1-x)^{-3}\), we substitute \(n = -3\) into the binomial series formula.The general term in the series is \[\binom{-3}{k} = \frac{(-3)(-3-1)(-3-2)...(-3-k+1)}{k!}.\] Calculate the first four binomial coefficients for \(k = 0, 1, 2, 3\).
03
Calculate the First Term (\(k = 0\))
The coefficient for \(k = 0\) is \[\binom{-3}{0} = 1.\] So, the first term is \[1.\]
04
Calculate the Second Term (\(k = 1\))
For \(k = 1\), the coefficient is \[\binom{-3}{1} = -3.\] Therefore, the second term is\[-3x.\]
05
Calculate the Third Term (\(k = 2\))
For \(k = 2\), the coefficient \[\binom{-3}{2} = \frac{-3 \cdot (-4)}{2!} = 6.\] Thus, the third term is\[6x^2.\]
06
Calculate the Fourth Term (\(k = 3\))
For \(k = 3\), the coefficient \[\binom{-3}{3} = \frac{-3 \cdot (-4) \cdot (-5)}{3!} = -10.\] So, the fourth term is\[-10x^3.\]
07
Combine the First Four Terms
Combining all the terms calculated together, the first four terms of the series are:\[1 - 3x + 6x^2 - 10x^3.\]
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Binomial Theorem
The Binomial Theorem is a cornerstone in algebra that allows us to expand expressions of the form \((1+x)^n\). It provides a way to express these powers as sums of terms involving binomial coefficients. Each term in the series has the format \(\binom{n}{k} x^k\), where \(\binom{n}{k}\) are the binomial coefficients. This theorem is particularly powerful because it works not only for positive integers but also for any real number \(n\) when using the binomial series expansion:
\[(1+x)^n = \sum_{k=0}^{\infty} \binom{n}{k} x^k\].
Some key applications and characteristics are:
\[(1+x)^n = \sum_{k=0}^{\infty} \binom{n}{k} x^k\].
Some key applications and characteristics are:
- When \(n\) is a positive integer, the series becomes finite, making it a simple polynomial.
- For other real values, the expansion continues infinitely as a series, valid for \(|x| < 1\).
Binomial Coefficients
Binomial Coefficients are denoted as \(\binom{n}{k}\) and represent the coefficients in the binomial expansion. They appear in each term of a binomial series and hold special mathematical significance. The formula for binomial coefficients is:
\[\binom{n}{k} = \frac{n(n-1)(n-2)...(n-k+1)}{k!}\],
where \(k!\) is the factorial of \(k\). Understanding these coefficients is key to applying the Binomial Theorem, and they have unique properties:
\[\binom{n}{k} = \frac{n(n-1)(n-2)...(n-k+1)}{k!}\],
where \(k!\) is the factorial of \(k\). Understanding these coefficients is key to applying the Binomial Theorem, and they have unique properties:
- Symmetry Property: \(\binom{n}{k} = \binom{n}{n-k}\), which simplifies calculations.
- Binomial coefficients count the number of ways to choose \(k\) items from \(n\) without regard to order, making them significant in combinatorics.
- They are integral to Pascal's Triangle, a convenient tool for remembering binomial coefficients quickly.
Infinite Series
An Infinite Series represents a sum of infinitely many terms. In the context of the Binomial Theorem, it describes how a power of a binomial can be expanded into an endless sequence of terms. This is applicable when \(n\) is not a non-negative integer, resulting in an expansion valid within a certain radius of convergence, \(|x| < 1\).
Key points about infinite series include:
Key points about infinite series include:
- An infinite series typically has no final term, though an initial portion can approximate the value.
- Convergence is crucial; the sum approaches a fixed value as more terms are added, so understanding the conditions for convergence is important.
- In practical use, only a finite number of initial terms may be calculated (like in our binomial series example, finding the first four terms).