Give an example of a 2 × 2 matrix where e₁ is an eigenvector, but e2 is not. Explain why your matrix has this property. (Hint: try an upper triangular matrix.)

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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**Example Problem: Eigenvectors of a 2x2 Matrix**

*Problem Statement:*

Give an example of a 2×2 matrix where **e₁** is an eigenvector, but **e₂** is not. Explain why your matrix has this property. (Hint: try an upper triangular matrix.)

---

*Explanation:*

To solve this problem, you will be looking for a 2x2 matrix form such that one of the standard basis vectors, **e₁**, is an eigenvector, while the other, **e₂**, is not. The hint suggests using an upper triangular matrix, which has the property that it can have less straightforward eigenvectors compared to diagonal matrices. 

Here’s an example of such a matrix:

\[ 
A = \begin{pmatrix}
\lambda & 1 \\
0 & \mu
\end{pmatrix}
\]

Where:
- \(\lambda\) and \(\mu\) are constants.
- **e₁** = (1, 0) is indeed an eigenvector with eigenvalue \(\lambda\).
- **e₂** = (0, 1) is not an eigenvector unless a new condition is added, which is typically not the case in this type of question.

In this matrix:
- **e₁** is an eigenvector because:

\[
A \cdot \mathbf{e}_1 = 
\begin{pmatrix}
\lambda & 1 \\
0 & \mu
\end{pmatrix}
\begin{pmatrix}
1 \\
0
\end{pmatrix}
=
\begin{pmatrix}
\lambda \\
0
\end{pmatrix}
=
\lambda \begin{pmatrix}
1 \\
0
\end{pmatrix}
\]

- **e₂** is not an eigenvector because the action of \(A\) on **e₂**:

\[
A \cdot \mathbf{e}_2 = 
\begin{pmatrix}
\lambda & 1 \\
0 & \mu
\end{pmatrix}
\begin{pmatrix}
0 \\
1
\end{pmatrix}
=
\begin{pmatrix}
1 \\
\mu
\end{pmatrix}
\]

results in a vector that cannot be written as \(\mu \times \mathbf{e}_2\), unless specific conditions hold
Transcribed Image Text:**Example Problem: Eigenvectors of a 2x2 Matrix** *Problem Statement:* Give an example of a 2×2 matrix where **e₁** is an eigenvector, but **e₂** is not. Explain why your matrix has this property. (Hint: try an upper triangular matrix.) --- *Explanation:* To solve this problem, you will be looking for a 2x2 matrix form such that one of the standard basis vectors, **e₁**, is an eigenvector, while the other, **e₂**, is not. The hint suggests using an upper triangular matrix, which has the property that it can have less straightforward eigenvectors compared to diagonal matrices. Here’s an example of such a matrix: \[ A = \begin{pmatrix} \lambda & 1 \\ 0 & \mu \end{pmatrix} \] Where: - \(\lambda\) and \(\mu\) are constants. - **e₁** = (1, 0) is indeed an eigenvector with eigenvalue \(\lambda\). - **e₂** = (0, 1) is not an eigenvector unless a new condition is added, which is typically not the case in this type of question. In this matrix: - **e₁** is an eigenvector because: \[ A \cdot \mathbf{e}_1 = \begin{pmatrix} \lambda & 1 \\ 0 & \mu \end{pmatrix} \begin{pmatrix} 1 \\ 0 \end{pmatrix} = \begin{pmatrix} \lambda \\ 0 \end{pmatrix} = \lambda \begin{pmatrix} 1 \\ 0 \end{pmatrix} \] - **e₂** is not an eigenvector because the action of \(A\) on **e₂**: \[ A \cdot \mathbf{e}_2 = \begin{pmatrix} \lambda & 1 \\ 0 & \mu \end{pmatrix} \begin{pmatrix} 0 \\ 1 \end{pmatrix} = \begin{pmatrix} 1 \\ \mu \end{pmatrix} \] results in a vector that cannot be written as \(\mu \times \mathbf{e}_2\), unless specific conditions hold
Expert Solution
Step 1

A non zero vector x is an eigen vector of a square matrix A if Ax = λ x  where λ is a scalar

Then λ is called the eigen value of A and x is the eigen vector corresponding to eigen value λ

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