Calculus (3rd Edition)

Published by W. H. Freeman
ISBN 10: 1464125260
ISBN 13: 978-1-46412-526-3

Chapter 11 - Infinite Series - 11.7 Taylor Series - Exercises - Page 588: 32

Answer

$\sin (3x)=\Sigma_{n = 0}^{\infty} (-1)^n \dfrac{(x-\pi/2)^{2n}}{(2n!)}$; converges for all $x$ with convergence interval $(-\infty,\infty)$.

Work Step by Step

The Taylor`s Series can be represented as: : $T(x)=\Sigma_{n = 0}^{\infty} \dfrac{f^n (c)}{n!}(x-c)^n$ If we consider $c=0$, then Taylor`s Series, $T(x)$ is also called as Maclaurin Series and the Maclaurin series for $f(x)$ is as given below: $f(x)=f(0)+f^{\prime}(0) x+\dfrac{f^{\prime \prime}(0) x^2}{2!}+\dfrac{f^{\prime \prime \prime}(0) x^3}{3!}+\dfrac{f^{\prime \prime \prime \prime}(0) x^4}{4!}+..............$ From Table $2$, we see that $f(x)=\cos x=\Sigma_{n = 0}^{\infty}(-1)^n\dfrac{x^{2n}}{(2n!)}=1-\dfrac{x^2}{2!}+\dfrac{x^4}{4!}-\dfrac{x^6}{6!}.....$; converges for $x$ Now, Taylor`s Series becomes: $f(x)=\sin x=\cos (x-\pi/2)=\Sigma_{n = 0}^{\infty} (-1)^n \dfrac{(x-\pi/2)^{2n}}{(2n!)}$; converges for $x$ Thus, we have the Taylor`s Series: $\sin (3x)=\Sigma_{n = 0}^{\infty} (-1)^n \dfrac{(x-\pi/2)^{2n}}{(2n!)}$; converges for all $x$ with convergence interval $(-\infty,\infty)$.
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