Chapter 1: Problem 1
Aufgabe \(1.4\) Man berechne die beiden folgenden Determinanten (vgl. dazu auch Abschnitt 1.6.1): A. \(\Delta=\left|\begin{array}{ccc}1 & 0 & -1 \\ 3 & 1 & -3 \\ 1 & 2 & -2\end{array}\right|\) B. \(\Delta=\left|\begin{array}{rrrr}1 & 2 & -4 & 4 \\ 3 & 6 & 9 & 0 \\ -2 & 8 & 1 & 9 \\ 4 & 2 & -2 & 0\end{array}\right|\).
Short Answer
Step by step solution
Calculate Determinant A
Calculate Determinant B using Laplace Expansion
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Matrix Calculations
To find the determinant of a 3x3 matrix, we use the formula:
- Identify the elements of the matrix as: \( \begin{array}{ccc} a & b & c \ d & e & f \ g & h & i \end{array} \).
- Apply the formula: \[ \Delta = a(ei - fh) - b(di - fg) + c(dh - eg) \].
- Calculate each term separately and then combine.
Cofactor Expansion
The method involves selecting one row or column and expanding it into minors and cofactors. Each minor is a smaller matrix, obtained by removing the row and column of a chosen element. Here’s a step-by-step breakdown:
- Select a row or column to expand—usually the one with the most zeros if possible.
- For each element in that row or column, calculate the minor determinant, which is the determinant of the 3x3 matrix that remains after removing the elements' row and column.
- Alternate the signs starting with a positive for the first element. For a first row expansion, use the pattern: positive, negative, positive, negative.
- Compute the final determinant by summing all the products of the elements and their cofactor expansions.
Linear Algebra
Determinants provide vital information about a matrix:
- They determine whether a matrix has an inverse (a non-zero determinant indicates an invertible matrix).
- They give insight into the scaling factor of linear transformations represented by the matrix.
- The sign of the determinant can indicate orientation (positive for preserving orientation, negative for reversing it).