# problem of fourier series

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#### Bhuvanesh123

Choose the function f(t) ; −∞ < ? < +∞, for which a Fourier series cannot be defined.
(a) 3 sin(25t?) (b) 4 cos(20t? + 3) + 2 sin (10?t)
(c) e-|t| sin(25?t) (d) 1

fourier series are available for all periodic signal .its obvious that all the four are periodic.But somewhere i hear that fourier series is not possible for constant .could someone give me hint for the answer ,so try to come up. Thank you

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#### _Eduardo_

##### Full Member level 5
Only (c) function is non periodic.

The general form of Fourier series is $a_0+a_1\cos(wt)+a_2\cos(2wt)+\cdots+b_1\sin(wt)+b_2\sin(2wt)+\cdots$

then (d) is a series with $a_0=1$ and the rest 0.

#### KlausST

##### Super Moderator
Staff member
Hi,

But somewhere i hear that fourier series is not possible for constant

so d) is constant.

And fourier analysis is possible. The result is: a0 = 1 , all other values are zero.

Klaus

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