Radius and interval of convergence Determine the radius and interval of convergence of the following power series. x-frac{x^3}{4}+frac{x^5}{9}-frac{x^7}{16}+...

jernplate8

jernplate8

Answered question

2020-10-23

Radius and interval of convergence Determine the radius and interval of convergence of the following power series.
xx34+x59x716+...

Answer & Explanation

pivonie8

pivonie8

Skilled2020-10-24Added 91 answers

First write the given series in formula:

S=xx34+x59x716+...

S=xx322+x533x744+...

S=x2(1)112x2(2)122+x2(3)132x2(4)142+...

S=n=1(1)n+1n2x2n1

Use the ratio test to determine whether the series is converging or diverging.

If |an+1an|q eventually for some 0, then n=1|an| converges.

If |an+1an|>1 eventually then n=1an diverges

Consider the given series:

f(x)=n=1(1)n+1n2x2n1

ak=(1)k+1k222k1

ak+1=(1)k+2(k+1)2x2k+21

=(1)k+2(k+1)2x2k+1

ak+1ak=(1)k+2(k+1)2x2k+1(1)k+1k2x2k1

=(1)k+2k1k2(k+1)2x2k+12k+1

=(1)k2(k+1)2x2

L=limk|ak+1ak|

=limk|(1)k2(k+1)2x2|

=|x2|

From ratio test, if L>1 series diverges.

L<1 series converges.

|x|<11x1 series converges.

Radius of convergence, R=1

Find the interval of convergence.

1x1

Interval of convergence ={x:x=1x1}

Interval of convergence [1,1]

Jeffrey Jordon

Jeffrey Jordon

Expert2021-12-27Added 2605 answers

Answer is given below (on video)

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