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Assume that \(A\) and \(B\) are \(n \times n\) matrices with det \(A=3\) and det \(B=-2 .\) Find the indicated determinants. \(\operatorname{det}(A B)\)

Short Answer

Expert verified
The determinant of the product \( AB \) is \(-6\).

Step by step solution

01

Understanding the Problem

We need to find the determinant of the product of two matrices \( A \) and \( B \). We are given the determinants of each individual matrix: \( \text{det}(A) = 3 \) and \( \text{det}(B) = -2 \).
02

Applying Property of Determinants

One of the key properties of determinants is that the determinant of a product of two matrices is equal to the product of their determinants. That is, \( \text{det}(A \times B) = \text{det}(A) \times \text{det}(B) \).
03

Calculate the Determinant of the Product

Using the property from the previous step, substitute the known values: \( \text{det}(A \times B) = \text{det}(A) \times \text{det}(B) = 3 \times (-2) \).
04

Compute the Result

Perform the multiplication: \( 3 \times (-2) = -6 \). Thus, \( \text{det}(AB) = -6 \).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Determinant Properties
When working with determinants, there are a few key properties that can help unravel complex matrix calculations. One fundamental property is that the determinant of a product of two matrices is equal to the product of their determinants. This can be expressed as:
  • If we have two matrices, \( A \) and \( B \), both \( n \times n \), the determinant of their product is \( \text{det}(A \times B) = \text{det}(A) \times \text{det}(B) \).
  • This property is particularly useful because it allows us to find the determinant of complex matrices by breaking them down into simpler components.
Moreover, the determinant can also help in understanding whether a matrix is invertible. When the determinant of a matrix is zero, it indicates that the matrix is singular and does not have an inverse. Understanding and applying these properties can significantly simplify solving matrix-related problems in linear algebra.
Matrix Multiplication
Matrix multiplication is a fundamental operation in linear algebra with widespread applications across fields like computer graphics, physics, and economics. To perform matrix multiplication, follow these steps:
  • Ensure the number of columns in the first matrix matches the number of rows in the second matrix.
  • The product of an \( m \times n \) matrix and an \( n \times p \) matrix will result in an \( m \times p \) matrix.
  • To obtain an entry in the resulting matrix, multiply elements from the rows of the first matrix by the corresponding elements from the columns of the second matrix, and sum the results.
This process can be complex, but practicing will help cement understanding. It's helpful to visualize each row and column to better see how they contribute to the final product. Remember, matrix multiplication is not commutative, which means \( A \times B \) is generally not the same as \( B \times A \). This nuance is crucial when calculating determinants, as seen in the properties of determinants.
Linear Algebra
Linear algebra is a branch of mathematics focusing on vectors, vector spaces (also known as linear spaces), linear mappings, and systems of linear equations. It's essential for anyone studying mathematics, physics, computer science, and engineering. Linear algebra simplifies complex structures into manageable computations. Here’s why it’s important:
  • It provides tools for solving systems of linear equations efficiently using techniques like Gaussian elimination and matrix operations.
  • It underlies algorithms for computer graphics, enabling 3D rotations and transformations.
  • In data science, linear algebra is crucial for operations like regression analysis and PCA (Principal Component Analysis).
The concepts of matrices and determinants are fundamental here, as they allow for compact and scalable computation processes. Linear algebra helps provide a theoretical foundation that supports numerous applications and technologies in our daily lives. Engaging deeply with these concepts can yield greater insights and problem-solving skills in various fields.

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Most popular questions from this chapter

If \(A\) is an invertible \(n \times n\) matrix, show that adj \(A\) is also invertible and that \\[ (\operatorname{adj} A)^{-1}=\frac{1}{\operatorname{det} A} A=\operatorname{adj}\left(A^{-1}\right) \\]

It can be shown that a nonnegative \(n \times n\) matrix is irreducible if and only if \((I+A)^{n-1}>0 .\) Use this criterion to determine whether the matrix \(A\) is irreducible. If \(A\) is reducible, find a permutation of its rows and columns that puts \(A\) into the block form \\[ \left[\begin{array}{ll} B & C \\ O & D \end{array}\right] \\] $$A=\left[\begin{array}{llll} 0 & 0 & 1 & 0 \\ 0 & 0 & 1 & 1 \\ 1 & 0 & 0 & 0 \\ 1 & 1 & 0 & 0 \end{array}\right]$$

Many species of seal have suffered from commercial hunting. They have been killed for their skin, blubber, and meat. The fur trade, in particular, reduced some seal populations to the point of extinction. Today, the greatest threats to seal populations are decline of fish stocks due to overfishing, pollution, disturbance of habitat, entanglement in marine debris, and culling by fishery owners. Some seals have been declared endangered species; other species are carefully managed. Table 4.7 gives the birth and survival rates for the northern fur seal, divided into 2 -year age classes. [The data are based on A. E. York and J. R. Hartley, "Pup Production Following Harvest of Female Northern Fur Seals," Canadian Journal of Fisheries and Aquatic Science, \(38(1981),\) pp. \(84-90 .\) $$\begin{array}{ccc} \text { Age (years) } & \text { Birth Rate } & \text { Survival Rate } \\ \hline 0-2 & 0.00 & 0.91 \\ 2-4 & 0.02 & 0.88 \\ 4-6 & 0.70 & 0.85 \\ 6-8 & 1.53 & 0.80 \\ 8-10 & 1.67 & 0.74 \\ 10-12 & 1.65 & 0.67 \\ 12-14 & 1.56 & 0.59 \\ 14-16 & 1.45 & 0.49 \\ 16-18 & 1.22 & 0.38 \\ 18-20 & 0.91 & 0.27 \\ 20-22 & 0.70 & 0.17 \\ 22-24 & 0.22 & 0.15 \\ 24-26 & 0.00 & 0.00 \end{array}$$ (a) Construct the Leslie matrix \(L\) for these data and compute the positive eigenvalue and a corresponding positive eigenvector. (b) In the long run, what percentage of seals will be in each age class and what will the growth rate be?

Solve the recurrence relation with the given initial conditions. $$b_{0}=0, b_{1}=1, b_{n}=2 b_{n-1}+2 b_{n-2} \text { for } n \geq 2$$

Use the power method to approximate the dominant eigenvalue and eigenvector of A to two decimal-place accuracy. Choose any initial vector you like (but keep the first Remark on page 326 in mind!) and apply the method until the digit in the second decimal place of the iterates stops changing. $$A=\left[\begin{array}{rrr} 12 & 6 & -6 \\ 2 & 0 & -2 \\ -6 & 6 & 12 \end{array}\right]$$

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