Compute the indicated 3 x 3 determinant. ab 0 0 a b a 0 b

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
Section: Chapter Questions
Problem 1RQ
Question
**Problem Statement:**
Compute the indicated \(3 \times 3\) determinant:

\[
\begin{vmatrix}
a & b & 0 \\
0 & a & b \\
a & 0 & b \\
\end{vmatrix}
\]

**Steps to Compute the Determinant:**

To find the determinant of a \(3 \times 3\) matrix, use the rule of Sarrus or the cofactor expansion method. Here, we’ll use the cofactor expansion along the first row:

1. The matrix is:

\[
\begin{pmatrix}
a & b & 0 \\
0 & a & b \\
a & 0 & b \\
\end{pmatrix}
\]

2. The determinant can be computed as:

\[
\text{det}(M) = a \begin{vmatrix} a & b \\ 0 & b \end{vmatrix} - b \begin{vmatrix} 0 & b \\ a & b \end{vmatrix} + 0 \begin{vmatrix} 0 & a \\ a & 0 \end{vmatrix}
\]

3. Calculate each of the \(2 \times 2\) determinants:

   - \(\begin{vmatrix} a & b \\ 0 & b \end{vmatrix} = ab - 0 = ab\)

   - \(\begin{vmatrix} 0 & b \\ a & b \end{vmatrix} = 0 \cdot b - a \cdot b = -ab\)

4. Substitute back into the original equation:

\[
\text{det}(M) = a(ab) - b(-ab) = a^2b + ab^2
\]

5. The final result is:

\[
\text{det}(M) = ab(a + b)
\] 

This determinant evaluates to the product of \(ab\) multiplied by the sum of \(a\) and \(b\).
Transcribed Image Text:**Problem Statement:** Compute the indicated \(3 \times 3\) determinant: \[ \begin{vmatrix} a & b & 0 \\ 0 & a & b \\ a & 0 & b \\ \end{vmatrix} \] **Steps to Compute the Determinant:** To find the determinant of a \(3 \times 3\) matrix, use the rule of Sarrus or the cofactor expansion method. Here, we’ll use the cofactor expansion along the first row: 1. The matrix is: \[ \begin{pmatrix} a & b & 0 \\ 0 & a & b \\ a & 0 & b \\ \end{pmatrix} \] 2. The determinant can be computed as: \[ \text{det}(M) = a \begin{vmatrix} a & b \\ 0 & b \end{vmatrix} - b \begin{vmatrix} 0 & b \\ a & b \end{vmatrix} + 0 \begin{vmatrix} 0 & a \\ a & 0 \end{vmatrix} \] 3. Calculate each of the \(2 \times 2\) determinants: - \(\begin{vmatrix} a & b \\ 0 & b \end{vmatrix} = ab - 0 = ab\) - \(\begin{vmatrix} 0 & b \\ a & b \end{vmatrix} = 0 \cdot b - a \cdot b = -ab\) 4. Substitute back into the original equation: \[ \text{det}(M) = a(ab) - b(-ab) = a^2b + ab^2 \] 5. The final result is: \[ \text{det}(M) = ab(a + b) \] This determinant evaluates to the product of \(ab\) multiplied by the sum of \(a\) and \(b\).
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