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Ch. 11 - Power Series
Briggs - Calculus: Early Transcendentals 3rd Edition
Briggs3rd EditionCalculus: Early TranscendentalsISBN: 9780136847243당신이 사용하는 게 아니라요?교과서 변경
11장, 문제 11.R.65d

Approximating ln 2 Consider the following three ways to approximate
ln 2.
d. At what value of x should the series in part (c) be evaluated to approximate ln 2? Write the resulting infinite series for ln 2.

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1
Recall that the natural logarithm function \( \ln(1+x) \) can be expressed as a power series centered at \( x=0 \), given by the Taylor series: \[ \ln(1+x) = \sum_{n=1}^{\infty} (-1)^{n+1} \frac{x^n}{n} = x - \frac{x^2}{2} + \frac{x^3}{3} - \frac{x^4}{4} + \cdots \]
To approximate \( \ln 2 \), recognize that \( \ln 2 = \ln(1 + 1) \). This means we want to evaluate the series at \( x = 1 \).
Substitute \( x = 1 \) into the series to write the infinite series representation for \( \ln 2 \): \[ \ln 2 = \sum_{n=1}^{\infty} (-1)^{n+1} \frac{1^n}{n} = 1 - \frac{1}{2} + \frac{1}{3} - \frac{1}{4} + \cdots \]
This alternating series converges to \( \ln 2 \), and each partial sum provides an approximation of \( \ln 2 \).
Thus, the value of \( x \) to evaluate the series at is \( x = 1 \), and the resulting infinite series for \( \ln 2 \) is the alternating harmonic series as shown above.

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주요 개념

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Taylor and Maclaurin Series

Taylor and Maclaurin series express functions as infinite sums of polynomial terms based on derivatives at a specific point. The Maclaurin series is a special case centered at zero. These series allow approximation of functions like ln(x) near a point by summing terms involving powers of (x - a).
추천 영상:
08:26
Convergence of Taylor & Maclaurin Series

Choosing the Expansion Point

Selecting the value of x (or the center a) for evaluating a series is crucial for accurate approximation. For ln 2, choosing x close to 1 or another convenient point simplifies the series and improves convergence. The choice affects the form and convergence speed of the infinite series.
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가이드 코스
07:51
Choosing a Convergence Test

Infinite Series Representation of ln(2)

The natural logarithm ln(2) can be represented as an infinite series derived from the Taylor or Maclaurin expansion of ln(1 + x). For example, ln(2) = ln(1 + 1) can be expressed as the alternating series 1 - 1/2 + 1/3 - 1/4 + ..., which converges to ln(2). Understanding this series helps in approximating ln(2) numerically.
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가이드 코스
06:52
Convergence of an Infinite Series