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Ch. 11 - Power Series
Briggs - Calculus: Early Transcendentals 3rd Edition
Briggs3rd EditionCalculus: Early TranscendentalsISBN: 9780136847243Non è quello che usi tu?Cambia libro di testo
Capitolo 11, Problema 11.4.79b

{Use of Tech} Fresnel integrals The theory of optics gives rise to the two Fresnel integrals
S(x) = ∫₀ˣ sin t² dt and C(x) = ∫₀ˣ cos t² dt
b. Expand sin t² and cos t² in a Maclaurin series, and then integrate to find the first four nonzero terms of the Maclaurin series for S and C.

Guida verificata passo dopo passo
1
Recall the Maclaurin series expansions for sine and cosine functions: \( \sin z = \sum_{n=0}^\infty (-1)^n \frac{z^{2n+1}}{(2n+1)!} \) and \( \cos z = \sum_{n=0}^\infty (-1)^n \frac{z^{2n}}{(2n)!} \).
Substitute \( z = t^2 \) into these series to get the expansions for \( \sin t^2 \) and \( \cos t^2 \): \[ \sin t^2 = \sum_{n=0}^\infty (-1)^n \frac{t^{4n+2}}{(2n+1)!} \quad \text{and} \quad \cos t^2 = \sum_{n=0}^\infty (-1)^n \frac{t^{4n}}{(2n)!} \].
Write out the first four nonzero terms explicitly for both series: For \( \sin t^2 \): \[ t^2 - \frac{t^6}{3!} + \frac{t^{10}}{5!} - \frac{t^{14}}{7!} + \cdots \] For \( \cos t^2 \): \[ 1 - \frac{t^4}{2!} + \frac{t^8}{4!} - \frac{t^{12}}{6!} + \cdots \].
Integrate each term of the series for \( \sin t^2 \) from 0 to \( x \) to find the Maclaurin series for \( S(x) = \int_0^x \sin t^2 \, dt \): \[ \int_0^x t^{m} dt = \frac{x^{m+1}}{m+1} \], so integrate term-by-term accordingly.
Similarly, integrate each term of the series for \( \cos t^2 \) from 0 to \( x \) to find the Maclaurin series for \( C(x) = \int_0^x \cos t^2 \, dt \), again using term-by-term integration and the power rule for integrals.

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Fresnel Integrals

Fresnel integrals S(x) and C(x) are defined as integrals of sine and cosine functions with quadratic arguments, specifically S(x) = ∫₀ˣ sin(t²) dt and C(x) = ∫₀ˣ cos(t²) dt. They arise in optics and wave theory, describing diffraction patterns and wave propagation.
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Maclaurin Series Expansion

A Maclaurin series is a Taylor series expansion of a function about zero. It expresses functions as infinite sums of powers of the variable, with coefficients derived from derivatives at zero. Expanding sin(t²) and cos(t²) into Maclaurin series involves substituting t² into the known series for sine and cosine.
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Term-by-Term Integration of Power Series

Once sin(t²) and cos(t²) are expanded into power series, integrating term-by-term from 0 to x is valid under uniform convergence. This process yields the Maclaurin series for S(x) and C(x) by integrating each power of t individually, resulting in a series representation for the Fresnel integrals.
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