Chapter 8: Problem 46
In each of Exercises 43-48, write Newton's binomial series for the given expression up to and including the \(x^{3}\) term. $$ 1 /(1+x) $$
Short Answer
Expert verified
The series is \(1 - x + x^2 - \frac{1}{2}x^3\).
Step by step solution
01
Recall the Binomial Series Formula
The binomial series expansion for \((1 + x)^{-n}\) is given by \(1 - nx + \frac{n(n+1)}{2!}x^2 - \frac{n(n+1)(n+2)}{3!}x^3 + \ldots\). For our expression, we want the series for \(1/(1+x)\), which can be rewritten as \((1+x)^{-1}\).
02
Substitute into the Binomial Formula
Substitute \(n = 1\) (since we have \((1+x)^{-1}\)) into the binomial series formula: \[1 - 1x + \frac{1(1+1)}{2!}x^2 - \frac{1(1+1)(1+2)}{3!}x^3 + \ldots \]
03
Evaluate the Terms Up to \(x^3\)
Evaluate each term of the series up to \(x^3\):- Zero order term: \(1\)- First order term: \(-x\)- Second order term: \(\frac{1 \times 2}{2}x^2 = x^2\)- Third order term: \(-\frac{1 \times 2 \times 3}{6}x^3 = -\frac{1}{2}x^3\)
04
Write the Final Series Expression
Combine all the evaluated terms to write the series up to the \(x^3\) term:\[1 - x + x^2 - \frac{1}{2}x^3\]
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Newton's Binomial Theorem
Newton's Binomial Theorem is a generalization of the Binomial Theorem. It's especially useful for expanding expressions raised to any power, including negative and fractional powers. Unlike the basic Binomial Theorem, which handles only non-negative integers, Newton's version allows a broader range of applications. This is useful for dealing with series expansions.
This allows us to express functions like \(1/(1+x)\) in an expanded form that's easier to handle analytically, similar to a polynomial.
- The binomial expression typically takes the form \((a + b)^n\).
- When \(n\) is a real number (not just whole numbers), we use Newton's Binomial Theorem.
- The series expansion becomes: \[(1 + x)^{-n} = 1 - nx + \frac{n(n+1)}{2!}x^2 - \frac{n(n+1)(n+2)}{3!}x^3 + \ldots\]
This allows us to express functions like \(1/(1+x)\) in an expanded form that's easier to handle analytically, similar to a polynomial.
Power Series Expansion
A power series is an infinite sum of terms in the form of \(a_nx^n\). This expression allows us to represent functions as infinite polynomials, enabling analysis and computation in calculus and potentially solving differential equations.
- A power series centered at zero is written as \(f(x) = a_0 + a_1x + a_2x^2 + a_3x^3 + \ldots\).
- The coefficients \(a_n\) are typically determined by the function that the series represents.
- Power series are closely related to Taylor and Maclaurin series, which are specialized forms of power series.
Taylor Series Expansion
The Taylor Series is a specific type of power series, which represents a function as an infinite sum of terms calculated from the values of its derivatives at a single point. Named after the mathematician Brook Taylor, it allows us to approximate functions around a given point.
- The general formula for a Taylor Series of a function \(f\) centered at \(a\) is: \[f(x) = f(a) + f'(a)(x-a) + \frac{f''(a)}{2!}(x-a)^2 + \cdots + \frac{f^{(n)}(a)}{n!}(x-a)^n + \cdots\]
- When the series is centered at zero, it becomes a Maclaurin series: \[f(x) = f(0) + f'(0)x + \frac{f''(0)}{2!}x^2 + \cdots + \frac{f^{(n)}(0)}{n!}x^n + \cdots\]
- For functions to be effectively approximated by Taylor series, they must be infinitely differentiable at the point of expansion.