How is the Sine Series Derived for Piecewise Functions?

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The discussion focuses on deriving the sine series for the piecewise function f(x) defined as 0 for x < 2 and 2 for x > 2, over the interval [0, 3]. The coefficients cn are calculated using integration, leading to a series representation involving sine functions. The final sine series expression incorporates terms that account for the discontinuity at x = 2, resulting in a combination of sine functions with specific coefficients. The confusion arises from the steps in the integration process and the evaluation of the series, but clarification is achieved through understanding the role of different n values in the sine series. The derivation illustrates the application of Fourier series to piecewise functions effectively.
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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
 
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my guess would be differnt N values
 
ok never mind i get it now
 
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