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Expand the same functions as in Problems 5.1 to 5.11 in Fourier series of complex exponentials einx on the interval(-Ï€,Ï€) and verify in each case that the answer is equivalent to the one found in Section 5.

Short Answer

Expert verified

The resultant expansion is π4+12∑n=-∞∞(-1)n-1πn2+in(-i)neinxn≠0.

Step by step solution

01

Given data

The given function is complex exponentials einx.

02

Concept of Fourier series

In terms of an infinite sum of sines and cosines, a Fourier series is an expansion of a periodic function.

The orthogonality relationships of the sine and cosine functions are used in Fourier series.

03

Find the coefficients

The c0 coefficient is shown below.

c0=12π∫0πxdxc0=π4

The other coefficients are as follows:

cn=12π∫0πxe-inxdxacn=12π-xine-inx+1n2e-inx-ππcn=12π-πineinπ+1n2e-inπ-cn=12πn2(-1)n+1+i2n(-i)n

Then the function is π4+12∑n=-∞∞(-1)n-1πn2+in(-i)neinxn≠0.

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Most popular questions from this chapter

In Problems 17to 20, find the Fourier sine transform of the function in the indicated problem, and write f(x)as a Fourier integral [use equation (12.14)]. Verify that the sine integral for f(x)is the same as the exponential integral found previously.

Problem 6.

In Problems 3 to 12, find the average value of the function on the given interval. Use equation (4.8) if it applies. If an average value is zero, you may be able to decide this from a quick sketch which shows you that the areas above and below the x axis are the same sin23xon(0,4Ï€).

(a) Represent as an exponential Fourier transform the function

f(x)={sinx,0<x<Ï€0,otherwise

Hint: write sinxin complex exponential form.

(b) Show that your result can be written as

f(x)=1π∫0∞cosαx+cosα(x−π)1−α2dα.

Given f(x)={x,0<x<1-2,1<x<2

a) Sketch at least three periods of the graph of the function represented by the sine series for f(x). Without finding any series, answer thefollowing question:

b) To what value does the sine series in (a) converge at x=1? At x=2? At x=0? At x=-1?

c)If the given function is continued with the period 2and then is represented by a complex exponential series ∑n=-∞∞Cne¾±²ÔÏ€³æ, what is the value of ∑n=−∞∞|cn|2?

Show that if (12.2) is written with the factor 12πmultiplying each integral, then the corresponding form of Parseval’s (12.24) theorem is ∫-∞∞|f(x)|2dx=∫-∞∞|g(α)|2dα.

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