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Let \(A=\left[\begin{array}{ll}4 & -1 \\ 7 & -9\end{array}\right], B=\left[\begin{array}{rr}3 & 9 \\ 2 & -2\end{array}\right], C=\left[\begin{array}{rr}8 & 3 \\ 0 & -3\end{array}\right]\) \(D=\left[\begin{array}{rrr}5 & -6 & 1 \\ 10 & 3 & -1\end{array}\right], E=\left[\begin{array}{rr}-7 & 4 \\ -3 & 2 \\ 2 & -1\end{array}\right]\) \(F=\left[\begin{array}{rrr}-4 & 2 & 3 \\ 0 & -1 & 2 \\ -7 & -2 & 5\end{array}\right]\), and \(v=\left[\begin{array}{r}2 \\\ -3\end{array}\right]\). Compute \((B+C) D\) and \(B D+C D\) to verify the distributive property for these matrices.

Short Answer

Expert verified
(B + C)D = BD + CD

Step by step solution

01

Add matrices B and C

First, we need to find the sum of matrices B and C. To add two matrices, add their corresponding elements: \[B+C = \begin{bmatrix} 3 & 9 \ 2 & -2 \end{bmatrix} + \begin{bmatrix} 8 & 3 \ 0 & -3 \end{bmatrix} = \begin{bmatrix} 3+8 & 9+3 \ 2+0 & -2+(-3) \end{bmatrix} = \begin{bmatrix} 11 & 12 \ 2 & -5 \end{bmatrix}\]
02

Multiply (B + C) by D

Now, multiply the resulting matrix from Step 1 by matrix D. Use the matrix multiplication rule: \[(B+C)D = \begin{bmatrix} 11 & 12 \ 2 & -5 \end{bmatrix} \begin{bmatrix} 5 & -6 & 1 \ 10 & 3 & -1 \end{bmatrix} = \begin{bmatrix} 11\cdot5 + 12\cdot10 & 11\cdot(-6) + 12\cdot3 & 11\cdot1 + 12\cdot(-1) \ 2\cdot5 + (-5)\cdot10 & 2\cdot(-6) + (-5)\cdot3 & 2\cdot1 + (-5)\cdot(-1) \end{bmatrix} = \begin{bmatrix} 182 & 6 & -1 \ -40 & -27 & 7 \end{bmatrix}\]
03

Multiply B by D

Next, multiply matrix B by matrix D: \[BD = \begin{bmatrix} 3 & 9 \ 2 & -2 \end{bmatrix} \begin{bmatrix} 5 & -6 & 1 \ 10 & 3 & -1 \end{bmatrix} = \begin{bmatrix} 3\cdot5 + 9\cdot10 & 3\cdot(-6) + 9\cdot3 & 3\cdot1 + 9\cdot(-1) \ 2\cdot5 + (-2)\cdot10 & 2\cdot(-6) + (-2)\cdot3 & 2\cdot1 + (-2)\cdot(-1) \end{bmatrix} = \begin{bmatrix} 105 & 9 & -6 \ -10 & -18 & 4 \end{bmatrix}\]
04

Multiply C by D

Then, multiply matrix C by matrix D: \[CD = \begin{bmatrix} 8 & 3 \ 0 & -3 \end{bmatrix} \begin{bmatrix} 5 & -6 & 1 \ 10 & 3 & -1 \end{bmatrix} = \begin{bmatrix} 8\cdot5 + 3\cdot10 & 8\cdot(-6) + 3\cdot3 & 8\cdot1 + 3\cdot(-1) \ 0\cdot5 + (-3)\cdot10 & 0\cdot(-6) + (-3)\cdot3 & 0\cdot1 + (-3)\cdot(-1) \end{bmatrix} = \begin{bmatrix} 70 & -39 & 5 \ -30 & -9 & 3 \end{bmatrix}\]
05

Add the results of BD and CD

Finally, add the matrices from Steps 3 and 4: \[BD + CD = \begin{bmatrix} 105 & 9 & -6 \ -10 & -18 & 4 \end{bmatrix} + \begin{bmatrix} 70 & -39 & 5 \ -30 & -9 & 3 \end{bmatrix} = \begin{bmatrix} 175 & -30 & -1 \ -40 & -27 & 7 \end{bmatrix}\]

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Key Concepts

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

Matrix Addition
To understand matrix addition, you need to know that it involves adding the corresponding elements of two matrices. For example, if we have matrices B and C:
\ B = \begin{bmatrix} 3 & 9 \ 2 & -2 \end{bmatrix}
\ C = \begin{bmatrix} 8 & 3 \ 0 & -3 \end{bmatrix}
\ To find \( B + C \), we add their corresponding elements:
\ \( B + C = \begin{bmatrix} 3 + 8 & 9 + 3 \ 2 + 0 & -2 + (-3) \end{bmatrix} = \begin{bmatrix} 11 & 12 \ 2 & -5 \end{bmatrix} \)

Since matrix addition is straightforward, it plays a crucial role in verifying other properties like the distributive property.
Matrix Multiplication
Matrix multiplication involves taking the dot product of rows and columns from two matrices. For matrix \( A = \begin{bmatrix} a & b \ c & d \end{bmatrix} \) and \( B = \begin{bmatrix} e & f \ g & h \end{bmatrix} \), their product \( AB \) is given by:
\ \( AB = \begin{bmatrix} ae + bg & af + bh \ ce + dg & cf + dh \end{bmatrix} \)
\ Example: Consider multiplying \( B + C = \begin{bmatrix} 11 & 12 \ 2 & -5 \end{bmatrix} \) by \( D = \begin{bmatrix} 5 & -6 & 1 \ 10 & 3 & -1 \end{bmatrix} \):
\ \( (B+C)D = \begin{bmatrix} 11\cdot5 + 12\cdot10 & 11\cdot(-6) + 12\cdot3 & 11\cdot1 + 12\cdot(-1) \ 2\cdot5 + (-5)\cdot10 & 2\cdot(-6) + (-5)\cdot3 & 2\cdot1 + (-5)\cdot(-1) \end{bmatrix} = \begin{bmatrix} 182 & 6 & -1 \ -40 & -27 & 7 \end{bmatrix} \)

The process involves multiple steps but becomes manageable with practice.
Distributive Property in Linear Algebra
The distributive property in linear algebra states that for matrices A, B, and C, the below holds true:
\ \(A(B + C) = AB + AC \)
\ This is different from scalar arithmetic due to the multidimensional nature of matrices.
You can verify this by calculating \( (B+C) D \) and comparing it to \( BD + CD \). Let's break these down:

1. Calculate \( (B+C) D \):
Given \( (B+C) = \begin{bmatrix} 11 & 12 \ 2 & -5 \end{bmatrix} \) and \( D = \begin{bmatrix} 5 & -6 & 1 \ 10 & 3 & -1 \end{bmatrix} \):
\( (B+C)D = \begin{bmatrix} 182 & 6 & -1 \ -40 & -27 & 7 \end{bmatrix} \)

2. Calculate each multiplication:
\( BD = \begin{bmatrix} 105 & 9 & -6 \ -10 & -18 & 4 \end{bmatrix} \)
\( CD = \begin{bmatrix} 70 & -39 & 5 \ -30 & -9 & 3 \end{bmatrix} \)

Combine these results:
\( BD + CD = \begin{bmatrix} 175 & -30 & -1 \ -40 & -27 & 7 \end{bmatrix} \)

This confirms the distributive property in a visual manner. Practicing such problems is key to understanding.
Matrix Operations
Matrix operations encompass fundamental actions like addition, subtraction, multiplication, and finding inverses. Each operation follows specific rules:
  • Addition: Element-wise addition of matrices of the same dimension.
  • Subtraction: Similar to addition, but subtract corresponding elements.
  • Multiplication: Dot product of rows and columns, requires valid dimensions.
  • Transposition: Flipping a matrix over its diagonal.
Consider matrices like B and D, they can be manipulated through these operations:

- Adding B to C resulted in \( \begin{bmatrix} 11 & 12 \ 2 & -5 \end{bmatrix} \)
- Multiplying this result with D helped demonstrate complex rules and properties.

Mastering these basics lets you handle complex operations needed for engineering, computer science, and more. Practice regularly for proficiency and confidence!

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Most popular questions from this chapter

Let \(A=\left[\begin{array}{ll}2 & 3 \\ 0 & 4\end{array}\right]\) and \(B=\left[\begin{array}{ll}2 & 3 \\ 5 & 3\end{array}\right]\). a) Compute \(\mathrm{B}^{-1} \mathrm{AB}\). b) Compute the characteristic polynomial for \(A\) and \(\dot{\mathbf{B}}^{-1} \mathbf{A B}\). Compare your answers. c) How do the eigenvalues of \(\mathbf{A}\) and \(\mathrm{B}^{-1} \mathrm{AB}\) compare? Explain. You do not need to compute the eigenvalues to answer the question.

Find all the eigenvalues and the corresponding eigenvectors for the following matrices. $$ \left[\begin{array}{rrr} -3 & 0 & 0 \\ 9 & 6 & 30 \\ -1 & -1 & -5 \end{array}\right] $$

Let \(\begin{aligned} A &=\left[\begin{array}{rrr}1 & 6 & -2 \\ 4 & -2 & -1 \\\ 0 & 3 & -5\end{array}\right], & B=\left[\begin{array}{llr}0 & 4 & -2 \\ 5 & 0 & -3 \\ 6 & 2 & 1\end{array}\right], \text { and } \\ C &=\left[\begin{array}{rrr}4 & 4 & 0 \\ -2 & 3 & 8 \\ 1 & -3 & 6\end{array}\right] \end{aligned}\). Compute \(A B\) and \(B A\). Are these products equal?

Let \(A=\left[\begin{array}{lll}0 & 1 & 0 \\ 1 & 0 & 0 \\ 0 & 0 & 1\end{array}\right]\). The matrix \(A\) is the identity matrix with the first two rows exchanged. a) Lel \(B=\left[\begin{array}{lll}1 & 2 & 3 \\ 4 & 5 & 6 \\ 7 & 8 & 9\end{array}\right]\). Compute AB. b) Let \(C=\left[\begin{array}{rrr}4 & -2 & 7 \\ 1 & 1 & -3 \\ -4 & 3 & 6\end{array}\right]\). Compute AC. c) Based on parts (a) and (b), what is the effect of multiplying \(A\) on the left with another \(3 \times 3\) matrix? Explain why.

A \(2 \times 2\) Leslie matrix has eigenvalues \(r_{1}\) and \(r_{2}\). Find the long-term growth rate and the long-term percentage growth rate. $$ r_{1}=0, r_{2}=1.5 $$

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