Let A = a b c d and let k be a scalar. Find a formula that relates det(kA) to k and det(A). Find det(A). det(A) = (Simplify your answer.)

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
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**Problem Statement**

Let \( A = \begin{bmatrix} a & b \\ c & d \end{bmatrix} \) and let \( k \) be a scalar. Find a formula that relates \( \text{det}(kA) \) to \( k \) and \( \text{det}(A) \).

---

**Steps to Solve**

1. **Find \(\text{det}(A)\):**

   The determinant of matrix \( A \) is calculated as:
   \[
   \text{det}(A) = ad - bc
   \]

(Simplify your answer.)


**Explanation**

To solve this problem, you need to understand how the determinant of a scalar multiple of a matrix, \( kA \), relates to \( k \) and the determinant of the original matrix, \( A \).

For a \( 2 \times 2 \) matrix, if you multiply the entire matrix by a scalar \( k \), the determinant of the resulting matrix \( kA \) is:
\[
\text{det}(kA) = k^2 \cdot \text{det}(A)
\]

This is because each row (or column) of the matrix is multiplied by the scalar \( k \), and since a determinant of a matrix involves the product of the elements of its rows and columns, the scalar appears as a multiplicative factor for each row (or column). For a \( 2 \times 2 \) matrix, this leads to the scalar being squared.

Use this relationship to determine how changing the scalar \( k \) affects the determinant of the matrix \( A \).
Transcribed Image Text:**Problem Statement** Let \( A = \begin{bmatrix} a & b \\ c & d \end{bmatrix} \) and let \( k \) be a scalar. Find a formula that relates \( \text{det}(kA) \) to \( k \) and \( \text{det}(A) \). --- **Steps to Solve** 1. **Find \(\text{det}(A)\):** The determinant of matrix \( A \) is calculated as: \[ \text{det}(A) = ad - bc \] (Simplify your answer.) **Explanation** To solve this problem, you need to understand how the determinant of a scalar multiple of a matrix, \( kA \), relates to \( k \) and the determinant of the original matrix, \( A \). For a \( 2 \times 2 \) matrix, if you multiply the entire matrix by a scalar \( k \), the determinant of the resulting matrix \( kA \) is: \[ \text{det}(kA) = k^2 \cdot \text{det}(A) \] This is because each row (or column) of the matrix is multiplied by the scalar \( k \), and since a determinant of a matrix involves the product of the elements of its rows and columns, the scalar appears as a multiplicative factor for each row (or column). For a \( 2 \times 2 \) matrix, this leads to the scalar being squared. Use this relationship to determine how changing the scalar \( k \) affects the determinant of the matrix \( A \).
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