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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 11.3.77

{Use of Tech} Approximating powers Compute the coefficients for the Taylor series for the following functions about the given point a, and then use the first four terms of the series to approximate the given number.
f(x) =∛x with a=64; approximate ∛60.

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1
Identify the function and the point about which to expand: here, the function is \(f(x) = \sqrt[3]{x} = x^{1/3}\) and the expansion point is \(a = 64\).
Compute the derivatives of \(f(x)\) up to the third order, since we want the first four terms of the Taylor series (which includes the function value and the first three derivatives). Use the power rule for derivatives: for \(f(x) = x^{1/3}\), the first derivative is \(f'(x) = \frac{1}{3} x^{-2/3}\), and so on.
Evaluate each derivative at the point \(x = 64\). This means calculating \(f(64)\), \(f'(64)\), \(f''(64)\), and \(f'''(64)\).
Write the Taylor series expansion formula centered at \(a=64\): \[ T_3(x) = f(64) + f'(64)(x - 64) + \frac{f''(64)}{2!}(x - 64)^2 + \frac{f'''(64)}{3!}(x - 64)^3 \] Substitute the values of the derivatives evaluated at 64 into this formula.
Use the Taylor polynomial \(T_3(x)\) to approximate \(f(60) = \sqrt[3]{60}\) by plugging in \(x = 60\) into the polynomial and simplifying the expression (without calculating the final numeric value).

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주요 개념

질문에 올바르게 답하기 위해 반드시 이해해야 하는 핵심 개념들은 다음과 같습니다.

Taylor Series Expansion

A Taylor series represents a function as an infinite sum of terms calculated from the derivatives of the function at a single point. It approximates the function near that point using polynomial terms, making complex functions easier to estimate.
추천 영상:
08:42
Taylor Series

Derivatives of Functions

Derivatives measure the rate of change of a function and are essential for finding the coefficients in a Taylor series. Calculating successive derivatives at the expansion point provides the terms needed for the polynomial approximation.
추천 영상:
06:30
Derivatives of Other Trig Functions

Approximation Using Partial Sums

Using only the first few terms of a Taylor series (partial sums) provides an approximation of the function near the expansion point. The accuracy depends on the number of terms and the distance from the point a; here, the first four terms approximate ∛60 near a=64.
추천 영상:
가이드 코스
08:01
Integration Using Partial Fractions
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교과서 질문

{Use of Tech} Newton's derivation of the sine and arcsine series Newton discovered the binomial series and then used it ingeniously to obtain many more results. Here is a case in point.

a. Referring to the figure, show that x = sin s or s = sin ⁻¹ x.

b. The area of a circular sector of radius r subtended by an angle θ is 1/2r²θ. Show that the area of the circular sector APE is s/2, which implies that

s = 2 ∫₀ˣ √(1 − t²) dt − x √(1 −x²)

c. Use the binomial series for f(x) = √(1 − x²) to obtain the first few terms of the Taylor series for s=sin ⁻¹ x.

d. Newton next inverted the series in part (c) to obtain the Taylor series for x=sin s. He did this by assuming sin s = ∑ aₖ sᵏ and solving x = sin(sin ⁻¹ x) for the coefficients aₖ. Find the first few terms of the Taylor series for sin s using this idea (a computer algebra system might be helpful as well).

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교과서 질문

Radius and interval of convergence Determine the radius and interval of convergence of the following power series.


∑ₖ₌₁∞ (3x + 2)ᵏ/k

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교과서 질문

Manipulating Taylor series Use the Taylor series in Table 11.5 to find the first four nonzero terms of the Taylor series for the following functions centered at 0.


sinh x²

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교과서 질문

Differential equations


a. Find a power series for the solution of the following differential equations, subject to the given initial condition

b. Identify the function represented by the power series.


y′(t) − y = 0, y(0) = 2

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교과서 질문

Remainders Find the remainder Rₙ for the nth−order Taylor polynomial centered at a for the given functions. Express the result for a general value of n.


f(x) = 1/(1 - x), a=0

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교과서 질문

Working with binomial series Use properties of power series, substitution, and factoring to find the first four nonzero terms of the Maclaurin series for the following functions. Use the Maclaurin series


(1 + x)⁻² = 1 − 2x + 3x² − 4x³ + ⋯, for −1 < x < 1.


(1 + 4x)⁻²

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