How is the Sine Series Derived for Piecewise Functions?

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SUMMARY

The sine series for the piecewise function f(x) defined as 0 for x < 2 and 2 for x > 2 on the interval [0, 3] is derived using Fourier series techniques. The coefficients cn are calculated using the formula cn = (2/L) ∫[0 to L] f(x) sin(nπx/L) dx, where L = 3. The integration results in a series that combines terms involving cosine functions evaluated at specific points, leading to the final expression f(x) = (4/π)(2/3 sin(πx/3) - (3/4)sin(2πx/3) + (2/3)sin(3πx/3) + ...). This derivation clarifies the behavior of the function across the defined intervals.

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hawaiidude
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why is

the sine series for f(x) = { 0 x<2 on 0,3
2 x>2

L=3

cn=2/3 int b=3 and a =0 f(x) sin( nxpi/ L)dx
= 2/3 int. b=2 a=0 (0) sin( pi n x/ 3) dx + 2/3 int b=3 a =2 (2) sin n x pi/3 dx
= 0 + 4/3{-3n pi cos n pi x/3} x=3 and x=2 = 4/n pi { cos 2 n pi/3 - cos n pi }

f(x)=sigma n=1 4/n pi { cos 2n pi/3 -(-1)^n sin n pi x

cos 2 pi/3=-1/2...

f(x)=4/pi( 2/3 sin pix/3-3/4sin2 pi x/3 +2/3sin 3 pi x/3...

how did they get this? very confused
 
Last edited by a moderator:
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my guess would be different N values
 
ok never mind i get it now
 

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