Let A= (11). It can be shown that etA - et Use this fact to write the solution to the initial value problem = Ay, y (0) = (9) Be sure to verify that your solution satisfies the initial value problem. -

Advanced Engineering Mathematics
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ISBN:9780470458365
Author:Erwin Kreyszig
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Chapter2: Second-order Linear Odes
Section: Chapter Questions
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q2. Linear algerba
### Linear Algebra and Matrix Theory Problems

1. **Eigenvalues of Matrices**

(a) Are the eigenvalues of \( AB \) necessarily all real? Justify your answer.

(b) Are the eigenvalues of \( AB \) necessarily all real? Justify your answer.
\[ \text{[Hint: Consider the matrices } A = \begin{pmatrix} 0 & 1 \\ 1 & 0 \end{pmatrix} \text{ and } B = \begin{pmatrix} 0 & i \\ -i & 0 \end{pmatrix}. \text{]} \]

2. **Solving Initial Value Problems Using Exponentiation of Matrices**

Let \( A = \begin{pmatrix} 1 & 1 \\ 0 & 1 \end{pmatrix} \). It can be shown that:
\[ e^{tA} = \begin{pmatrix} e^t & te^t \\ 0 & e^t \end{pmatrix}. \]

Use this fact to write the solution to the initial value problem:
\[ \begin{cases} 
y' = Ay, \\
y(0) = \begin{pmatrix} 0 \\ 1 \end{pmatrix}.
\end{cases} \]

Be sure to verify that your solution satisfies the initial value problem.

3. **Properties of Skew Hermitian Matrices**

Recall that a skew Hermitian matrix is a matrix \( B \) with the property \( B^H = -B \). Let \( B \) be an \( n \times n \) skew Hermitian matrix and let \( \mathbf{x} \) be a vector in \( \mathbb{C}^n \).

Show that \( \alpha = \mathbf{x}^H A \mathbf{x} \) is a purely imaginary number; that is, \( \alpha = bi \) with \( b \) a real number.

\[ \text{[Hint: Recall that for a complex number } z, \, z^H = \bar{z}. \]

### Explanation of Graphs and Diagrams

There are several matrices provided in the text:

- \( A = \begin{pmatrix} 0 & 1 \\ 1 & 0 \end{pmatrix} \)
- \( B = \begin{pmatrix} 0 & i \\ -i
Transcribed Image Text:### Linear Algebra and Matrix Theory Problems 1. **Eigenvalues of Matrices** (a) Are the eigenvalues of \( AB \) necessarily all real? Justify your answer. (b) Are the eigenvalues of \( AB \) necessarily all real? Justify your answer. \[ \text{[Hint: Consider the matrices } A = \begin{pmatrix} 0 & 1 \\ 1 & 0 \end{pmatrix} \text{ and } B = \begin{pmatrix} 0 & i \\ -i & 0 \end{pmatrix}. \text{]} \] 2. **Solving Initial Value Problems Using Exponentiation of Matrices** Let \( A = \begin{pmatrix} 1 & 1 \\ 0 & 1 \end{pmatrix} \). It can be shown that: \[ e^{tA} = \begin{pmatrix} e^t & te^t \\ 0 & e^t \end{pmatrix}. \] Use this fact to write the solution to the initial value problem: \[ \begin{cases} y' = Ay, \\ y(0) = \begin{pmatrix} 0 \\ 1 \end{pmatrix}. \end{cases} \] Be sure to verify that your solution satisfies the initial value problem. 3. **Properties of Skew Hermitian Matrices** Recall that a skew Hermitian matrix is a matrix \( B \) with the property \( B^H = -B \). Let \( B \) be an \( n \times n \) skew Hermitian matrix and let \( \mathbf{x} \) be a vector in \( \mathbb{C}^n \). Show that \( \alpha = \mathbf{x}^H A \mathbf{x} \) is a purely imaginary number; that is, \( \alpha = bi \) with \( b \) a real number. \[ \text{[Hint: Recall that for a complex number } z, \, z^H = \bar{z}. \] ### Explanation of Graphs and Diagrams There are several matrices provided in the text: - \( A = \begin{pmatrix} 0 & 1 \\ 1 & 0 \end{pmatrix} \) - \( B = \begin{pmatrix} 0 & i \\ -i
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