6) We call the matrix below the general 2 × 2 matrix because its entries could be any real numbers. a Find a formula (which will obviously involve a, b, c, and d) for the eigenvalues of the general 2×2 matrix. Find an equation which describes those 2x2 matrices that have only one eigenvalue, and gives three examples of such matrices (only one of your examples may be triangular)

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### Eigenvalues of a General 2x2 Matrix

#### Matrix Definition
We call the matrix below the **general 2 × 2 matrix** because its entries could be any real numbers.

\[ \begin{bmatrix} a & b \\ c & d \end{bmatrix} \]

#### Problem Description
1. **Formula for Eigenvalues**:
   - Find a formula (which will obviously involve \(a, b, c,\) and \(d\)) for the eigenvalues of the general 2 × 2 matrix.
2. **Equation for Matrices with Only One Eigenvalue**:
   - Find an equation that describes those 2 × 2 matrices that have only one eigenvalue.
3. **Examples**:
   - Provide three examples of such matrices (only one of your examples may be triangular).

#### Explanation

1. **Eigenvalue Formula**:
   To find the eigenvalues of a 2 × 2 matrix \(\begin{bmatrix} a & b \\ c & d \end{bmatrix}\), we use the characteristic equation:
   \[
   \text{det}(\mathbf{A} - \lambda \mathbf{I}) = 0
   \]
   where \(\mathbf{A} = \begin{bmatrix} a & b \\ c & d \end{bmatrix}\) and \(\mathbf{I}\) is the identity matrix \(\begin{bmatrix} 1 & 0 \\ 0 & 1 \end{bmatrix}\).

   The characteristic equation becomes:
   \[
   \left| \begin{array}{cc} a - \lambda & b \\ c & d - \lambda \end{array} \right| = 0
   \]

   Simplifying, we get the quadratic equation:
   \[
   \lambda^2 - (a + d)\lambda + (ad - bc) = 0
   \]

   The eigenvalues \(\lambda\) are the solutions to this quadratic equation:
   \[
   \lambda = \frac{(a + d) \pm \sqrt{(a + d)^2 - 4(ad - bc)}}{2}
   \]

2. **Equation for Matrices with One Eigenvalue**:
   For a matrix to have only one eigenvalue, the discriminant of the quadratic equation must be zero:
   \[
   (
Transcribed Image Text:### Eigenvalues of a General 2x2 Matrix #### Matrix Definition We call the matrix below the **general 2 × 2 matrix** because its entries could be any real numbers. \[ \begin{bmatrix} a & b \\ c & d \end{bmatrix} \] #### Problem Description 1. **Formula for Eigenvalues**: - Find a formula (which will obviously involve \(a, b, c,\) and \(d\)) for the eigenvalues of the general 2 × 2 matrix. 2. **Equation for Matrices with Only One Eigenvalue**: - Find an equation that describes those 2 × 2 matrices that have only one eigenvalue. 3. **Examples**: - Provide three examples of such matrices (only one of your examples may be triangular). #### Explanation 1. **Eigenvalue Formula**: To find the eigenvalues of a 2 × 2 matrix \(\begin{bmatrix} a & b \\ c & d \end{bmatrix}\), we use the characteristic equation: \[ \text{det}(\mathbf{A} - \lambda \mathbf{I}) = 0 \] where \(\mathbf{A} = \begin{bmatrix} a & b \\ c & d \end{bmatrix}\) and \(\mathbf{I}\) is the identity matrix \(\begin{bmatrix} 1 & 0 \\ 0 & 1 \end{bmatrix}\). The characteristic equation becomes: \[ \left| \begin{array}{cc} a - \lambda & b \\ c & d - \lambda \end{array} \right| = 0 \] Simplifying, we get the quadratic equation: \[ \lambda^2 - (a + d)\lambda + (ad - bc) = 0 \] The eigenvalues \(\lambda\) are the solutions to this quadratic equation: \[ \lambda = \frac{(a + d) \pm \sqrt{(a + d)^2 - 4(ad - bc)}}{2} \] 2. **Equation for Matrices with One Eigenvalue**: For a matrix to have only one eigenvalue, the discriminant of the quadratic equation must be zero: \[ (
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