Chapter 10: Problem 7
Find the first four terms of the binomial series for the functions. \begin{equation}\left(1+x^{3}\right)^{-1 / 2}\end{equation}
Short Answer
Expert verified
1 \(- \frac{1}{2}x^3 + \frac{3}{8}x^6 - \frac{5}{16}x^9\).
Step by step solution
01
Identify the Binomial Series Formula
The binomial series expansion formula is given by \[ (1 + x)^n = \sum_{k=0}^{fty} \binom{n}{k} x^k \] where \( \binom{n}{k} = \frac{n(n-1)(n-2)...(n-k+1)}{k!} \) is the generalized binomial coefficient. In this problem, our expression is \((1+x^3)^{-1/2}\), so \( n = -1/2 \) and \( x \) is replaced by \( x^3 \).
02
Apply the Formula for Each Term
We need to find the first four terms of the series. These terms correspond to \( k = 0, 1, 2, 3 \). Using the binomial coefficient formula, compute each term.1. First Term \( (k=0) \): \[ \binom{-1/2}{0} (x^3)^0 = 1 \]2. Second Term \( (k=1) \): \[ \binom{-1/2}{1} (x^3) = \left( -\frac{1}{2} \right) x^3 = -\frac{1}{2}x^3 \]3. Third Term \( (k=2) \): \[ \binom{-1/2}{2} (x^3)^2 = \frac{-1/2(-3/2)}{2!}(x^6) = \frac{3}{8}x^6 \]4. Fourth Term \( (k=3) \): \[ \binom{-1/2}{3} (x^3)^3 = \frac{-1/2(-3/2)(-5/2)}{3!}(x^9) = -\frac{5}{16}x^9 \]
03
Write Down the First Four Terms
Compile the results from Step 2 to write down the first four terms of the series:\[ 1 - \frac{1}{2}x^3 + \frac{3}{8}x^6 - \frac{5}{16}x^9 \]
04
Verification
Double-check each step to ensure the binomial coefficients and power of each term are calculated correctly. Ensure that calculations follow the pattern \( \binom{n}{k} x^{3k} \), confirming the logic and arithmetic are correctly applied.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Binomial Series
The Binomial Series is a representation of an expression raised to a power as a sum of terms. Specifically, it expands the expression \((1 + x)^n\) into a series:
- This series helps in approximating expressions that are generally difficult to compute.
- It is particularly useful when dealing with fractional or negative powers.
Generalized Binomial Coefficient
The Generalized Binomial Coefficient extends the idea of coefficients beyond non-negative integers. Normally, binomial coefficients \(\binom{n}{k}\) involve integers, but for the binomial series with noninteger powers:
- The coefficient is calculated using the expression: \(\binom{n}{k} = \frac{n(n-1)(n-2)...(n-k+1)}{k!}\).
- This formula works regardless of the value of \(n\), allowing us to expand series with any real number exponent.
Series Expansion
Series Expansion breaks an expression into a sum of terms with increasing powers of a variable. For binomial series, the series does not need to be finite and instead can be expressed to any desired number of terms following a pattern:
- The expression \((1 + x^3)^{-1/2}\) is expanded into terms \(k = 0, 1, 2, 3\), providing terms like \(1, -\frac{1}{2}x^3, \frac{3}{8}x^6, -\frac{5}{16}x^9\).
- This process illustrates how a complex expression can be approximated by simpler terms.
Binomial Coefficient Formula
The Binomial Coefficient Formula is central to calculating each term in a binomial series. It defines how we derive coefficients for expanded series terms:
- This formula is: \(\binom{n}{k} = \frac{n(n-1)(n-2)...(n-k+1)}{k!}\).
- While traditional binomial coefficients consider natural numbers, this formula's beauty is its application to fractional or negative exponents.