3. This matrix has repeated eigenvalues for which value(s) of a? Show your wor -1] a M 4

Linear Algebra: A Modern Introduction
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Chapter2: Systems Of Linear Equations
Section2.2: Direct Methods For Solving Linear Systems
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**3. This matrix has repeated eigenvalues for which value(s) of \(a\)? Show your work.**

Given the matrix \(M\):

\[ 
M = \begin{bmatrix} 
a & -1 \\ 
4 & 4 
\end{bmatrix} 
\]

(Show the matrix \(M\) above your solution.)

---

To find the value(s) of \(a\) for which the matrix \(M\) has repeated eigenvalues, let's follow these steps:

1. **Write the characteristic equation of the matrix \(M\).**

   The characteristic equation for a matrix \(M\) is given by the determinant of \((M - \lambda I) = 0\), where \(\lambda\) is an eigenvalue and \(I\) is the identity matrix:

\[ 
\text{det} \left( \begin{bmatrix} 
a & -1 \\ 
4 & 4 
\end{bmatrix} - \lambda \begin{bmatrix} 
1 & 0 \\ 
0 & 1 
\end{bmatrix} \right) = 0 
\]

2. **Subtract \(\lambda\) times the identity matrix from matrix \(M\):**

\[ 
M - \lambda I = \begin{bmatrix} 
a & -1 \\ 
4 & 4 
\end{bmatrix} - \begin{bmatrix} 
\lambda & 0 \\ 
0 & \lambda 
\end{bmatrix} = \begin{bmatrix} 
a - \lambda & -1 \\ 
4 & 4 - \lambda 
\end{bmatrix} 
\]

3. **Calculate the determinant of the resulting matrix:**

\[ 
\text{det} \left( \begin{bmatrix} 
a - \lambda & -1 \\ 
4 & 4 - \lambda 
\end{bmatrix} \right) = (a - \lambda)(4 - \lambda) - (-1 \cdot 4) 
\]

4. **Simplify the equation:**

\[ 
(a - \lambda)(4 - \lambda) + 4 = a(4 - \lambda) - \lambda (4 - \lambda) + 4 
\]
\[ 
= 4a - a\lambda - 4\lambda + \lambda^2 + 4
Transcribed Image Text:**3. This matrix has repeated eigenvalues for which value(s) of \(a\)? Show your work.** Given the matrix \(M\): \[ M = \begin{bmatrix} a & -1 \\ 4 & 4 \end{bmatrix} \] (Show the matrix \(M\) above your solution.) --- To find the value(s) of \(a\) for which the matrix \(M\) has repeated eigenvalues, let's follow these steps: 1. **Write the characteristic equation of the matrix \(M\).** The characteristic equation for a matrix \(M\) is given by the determinant of \((M - \lambda I) = 0\), where \(\lambda\) is an eigenvalue and \(I\) is the identity matrix: \[ \text{det} \left( \begin{bmatrix} a & -1 \\ 4 & 4 \end{bmatrix} - \lambda \begin{bmatrix} 1 & 0 \\ 0 & 1 \end{bmatrix} \right) = 0 \] 2. **Subtract \(\lambda\) times the identity matrix from matrix \(M\):** \[ M - \lambda I = \begin{bmatrix} a & -1 \\ 4 & 4 \end{bmatrix} - \begin{bmatrix} \lambda & 0 \\ 0 & \lambda \end{bmatrix} = \begin{bmatrix} a - \lambda & -1 \\ 4 & 4 - \lambda \end{bmatrix} \] 3. **Calculate the determinant of the resulting matrix:** \[ \text{det} \left( \begin{bmatrix} a - \lambda & -1 \\ 4 & 4 - \lambda \end{bmatrix} \right) = (a - \lambda)(4 - \lambda) - (-1 \cdot 4) \] 4. **Simplify the equation:** \[ (a - \lambda)(4 - \lambda) + 4 = a(4 - \lambda) - \lambda (4 - \lambda) + 4 \] \[ = 4a - a\lambda - 4\lambda + \lambda^2 + 4
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