[3] Find the Fourier series of the function given by f(x) = { f -a

Advanced Engineering Mathematics
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ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
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### Fourier Series Calculation and Graph Analysis

#### Problem Statement

**3.** Find the Fourier series of the function given by:

\[ 
f(x) = \begin{cases} 
0 & \text{if } -a < x < 0, \\
3x & \text{if } 0 < x < a.
\end{cases} 
\]

Sketch the graph of \( f(x) \) and its periodic extension. To what values does the Fourier series converge at \( x = -a \), \( x = -a/2 \), \( x = 0 \), \( x = a/2 \), \( x = a \), and \( x = 2a \)?

#### Explanation

##### Fourier Series

The Fourier series of a function \( f(x) \) is an expansion of the function in terms of sine and cosine functions. For a periodic function \( f(x) \) with period \( 2L \), the Fourier series is given by:

\[ 
f(x) \sim \frac{a_0}{2} + \sum_{n=1}^{\infty} \left( a_n \cos\left( \frac{n\pi x}{L} \right) + b_n \sin\left( \frac{n\pi x}{L} \right) \right), 
\]

where the coefficients \( a_0 \), \( a_n \), and \( b_n \) are calculated as follows:

\[ 
a_0 = \frac{1}{L} \int_{-L}^{L} f(x) \, dx,
\]

\[ 
a_n = \frac{1}{L} \int_{-L}^{L} f(x) \cos \left( \frac{n\pi x}{L} \right) \, dx,
\]

\[ 
b_n = \frac{1}{L} \int_{-L}^{L} f(x) \sin \left( \frac{n\pi x}{L} \right) \, dx.
\]

##### Graph Description

To sketch the function \( f(x) \) and its periodic extension, follow these steps:

1. For \( x \) in the interval \( -a < x < 0 \), the function \( f(x) \) is zero. This describes a horizontal line along the x-axis.
2. For
Transcribed Image Text:### Fourier Series Calculation and Graph Analysis #### Problem Statement **3.** Find the Fourier series of the function given by: \[ f(x) = \begin{cases} 0 & \text{if } -a < x < 0, \\ 3x & \text{if } 0 < x < a. \end{cases} \] Sketch the graph of \( f(x) \) and its periodic extension. To what values does the Fourier series converge at \( x = -a \), \( x = -a/2 \), \( x = 0 \), \( x = a/2 \), \( x = a \), and \( x = 2a \)? #### Explanation ##### Fourier Series The Fourier series of a function \( f(x) \) is an expansion of the function in terms of sine and cosine functions. For a periodic function \( f(x) \) with period \( 2L \), the Fourier series is given by: \[ f(x) \sim \frac{a_0}{2} + \sum_{n=1}^{\infty} \left( a_n \cos\left( \frac{n\pi x}{L} \right) + b_n \sin\left( \frac{n\pi x}{L} \right) \right), \] where the coefficients \( a_0 \), \( a_n \), and \( b_n \) are calculated as follows: \[ a_0 = \frac{1}{L} \int_{-L}^{L} f(x) \, dx, \] \[ a_n = \frac{1}{L} \int_{-L}^{L} f(x) \cos \left( \frac{n\pi x}{L} \right) \, dx, \] \[ b_n = \frac{1}{L} \int_{-L}^{L} f(x) \sin \left( \frac{n\pi x}{L} \right) \, dx. \] ##### Graph Description To sketch the function \( f(x) \) and its periodic extension, follow these steps: 1. For \( x \) in the interval \( -a < x < 0 \), the function \( f(x) \) is zero. This describes a horizontal line along the x-axis. 2. For
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