3. Fourier Trigonometric Series. -A

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
Section: Chapter Questions
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Can you help me with question 3?

**1. Boundary Value Problem with Nonhomogeneous ODE.**

For each choice of \( g(x) \) listed below, find all solutions to the following boundary value problem.

\[ 4y'' + \pi^2 y = g(x) \quad \text{for } 0 < x < 2, \quad y'(0) = 0, \, y'(2) = 0. \]

- (a) \( g(x) = 0 \)
- (b) \( g(x) = x \)

---

**2. Eigenvalue Problem with First Derivative in Linear Operator.**

Find the eigenvalues and eigenfunctions for the boundary value problem,

\[ y'' + 4y' + \lambda y = 0 \quad \text{on } 0 < x < \pi, \quad y'(0) = 0, \, y'(\pi) = 0. \]

---

**3. Fourier Trigonometric Series.**

Consider the function \( f(x) \) defined on \( (-\pi, \pi) \), 

\[ f(x) = \begin{cases} 
0, & -\pi < x < 0 \\
1, & 0 \leq x < \pi/2 \\
0, & \pi/2 \leq x < \pi 
\end{cases} \]

and its Fourier series

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

(a) Derive expressions for \( a_0, \, a_n \) and \( b_n \), for \( n = 1, 2, \ldots \).

(b) Write out the terms of the Fourier series through \( n = 5 \).

(c) Graph the periodic extension of \( f(x) \) on the interval \( (-3\pi, 3\pi) \) that represents the pointwise convergence of the Fourier series in part (b). At jump discontinuities, identify the value to which the series converges.

---

**4. Eigenvalue Problem for Cauchy-Euler Equation.**

Find the eigenvalues and eigenfunctions for the boundary value problem,

\[ 4x^2y'' + 4xy
Transcribed Image Text:**1. Boundary Value Problem with Nonhomogeneous ODE.** For each choice of \( g(x) \) listed below, find all solutions to the following boundary value problem. \[ 4y'' + \pi^2 y = g(x) \quad \text{for } 0 < x < 2, \quad y'(0) = 0, \, y'(2) = 0. \] - (a) \( g(x) = 0 \) - (b) \( g(x) = x \) --- **2. Eigenvalue Problem with First Derivative in Linear Operator.** Find the eigenvalues and eigenfunctions for the boundary value problem, \[ y'' + 4y' + \lambda y = 0 \quad \text{on } 0 < x < \pi, \quad y'(0) = 0, \, y'(\pi) = 0. \] --- **3. Fourier Trigonometric Series.** Consider the function \( f(x) \) defined on \( (-\pi, \pi) \), \[ f(x) = \begin{cases} 0, & -\pi < x < 0 \\ 1, & 0 \leq x < \pi/2 \\ 0, & \pi/2 \leq x < \pi \end{cases} \] and its Fourier series \[ f(x) \sim \frac{a_0}{2} + \sum_{n=1}^{\infty} \left( a_n \cos(nx) + b_n \sin(nx) \right). \] (a) Derive expressions for \( a_0, \, a_n \) and \( b_n \), for \( n = 1, 2, \ldots \). (b) Write out the terms of the Fourier series through \( n = 5 \). (c) Graph the periodic extension of \( f(x) \) on the interval \( (-3\pi, 3\pi) \) that represents the pointwise convergence of the Fourier series in part (b). At jump discontinuities, identify the value to which the series converges. --- **4. Eigenvalue Problem for Cauchy-Euler Equation.** Find the eigenvalues and eigenfunctions for the boundary value problem, \[ 4x^2y'' + 4xy
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