Multiplying a matrix by a matrix | Matrices | Precalculus

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In this lesson, we explored the process of multiplying two matrices, specifically matrix E and matrix D, ensuring that the multiplication is valid by confirming the dimensions. We calculated the resulting 2×2 matrix by taking the dot products of the rows of matrix E with the columns of matrix D, ultimately finding the product to be \(\begin{bmatrix} -1 & -6 \\ 7 & 10 \end{bmatrix}\). This example illustrates the systematic approach to matrix multiplication while adhering to the necessary rules.

Matrix Multiplication: Calculating the Product of Matrices E and D

In this article, we’ll dive into how to multiply two matrices, specifically matrix E and matrix D. We’ll go through the steps to calculate their product and make sure the multiplication is valid.

Understanding the Matrices

We have two matrices to work with:

  • Matrix E:

[
begin{bmatrix}
0 & 3 & 5 \
5 & 5 & 2
end{bmatrix}
]

  • Matrix D:

[
begin{bmatrix}
3 & 4 \
-2 & -2 \
1 & 0
end{bmatrix}
]

Validating the Multiplication

Before we start multiplying, we need to check if it’s possible. Matrix multiplication is only possible when the number of columns in the first matrix is the same as the number of rows in the second matrix.

  • Matrix E has 2 rows and 3 columns (2×3).
  • Matrix D has 3 rows and 2 columns (3×2).

Since matrix E has 3 columns and matrix D has 3 rows, we can multiply them. Remember, the order matters; ( E times D ) is different from ( D times E ).

Performing the Multiplication

When we multiply a 2×3 matrix by a 3×2 matrix, we get a 2×2 matrix. Each entry in the new matrix is found by taking the dot product of a row from matrix E and a column from matrix D.

Top Left Entry

To find the top left entry of the new matrix, calculate:

[
0 times 3 + 3 times -2 + 5 times 1 = 0 – 6 + 5 = -1
]

Top Right Entry

Next, for the top right entry:

[
0 times 4 + 3 times -2 + 5 times 0 = 0 – 6 + 0 = -6
]

Bottom Left Entry

For the bottom left entry, use the second row of matrix E and the first column of matrix D:

[
5 times 3 + 5 times -2 + 2 times 1 = 15 – 10 + 2 = 7
]

Bottom Right Entry

Finally, calculate the bottom right entry:

[
5 times 4 + 5 times -2 + 2 times 0 = 20 – 10 + 0 = 10
]

Resulting Matrix

After doing all the calculations, the resulting matrix is:

[
begin{bmatrix}
-1 & -6 \
7 & 10
end{bmatrix}
]

Conclusion

The product of matrix E and matrix D is:

[
begin{bmatrix}
-1 & -6 \
7 & 10
end{bmatrix}
]

This example shows how to systematically multiply matrices while following the rules of matrix multiplication.

  1. Reflect on the process of matrix multiplication described in the article. What steps did you find most challenging, and why?
  2. Consider the importance of validating matrix multiplication before performing it. How does this step impact the overall calculation process?
  3. Discuss how the order of matrices affects the result of matrix multiplication. Can you think of any real-world scenarios where this might be important?
  4. Analyze the method used to calculate each entry in the resulting matrix. How does understanding the dot product help in this process?
  5. Think about the final resulting matrix. What insights can you draw from the values obtained, and how might they be interpreted in a practical context?
  6. Reflect on your previous experiences with matrix multiplication. How did this article enhance your understanding or change your approach?
  7. Consider the role of matrices in various fields such as computer graphics, physics, or economics. How might the concepts discussed in the article apply to these areas?
  8. Imagine explaining the process of matrix multiplication to someone unfamiliar with the concept. What key points from the article would you emphasize to ensure clarity and understanding?
  1. Matrix Multiplication Race

    Challenge yourself and your classmates to a race! Pair up and see who can correctly calculate the product of two given matrices the fastest. Use the matrices E and D from the article as a starting point. This activity will help you practice the steps of matrix multiplication and improve your speed and accuracy.

  2. Create Your Own Matrices

    Design two matrices of your own and swap them with a classmate. Validate if their multiplication is possible, and then calculate the product. This activity encourages creativity and reinforces the concept of matrix dimensions and multiplication rules.

  3. Matrix Multiplication Puzzle

    Turn matrix multiplication into a puzzle! Write each step of the multiplication process on separate cards and mix them up. Challenge yourself to arrange the cards in the correct order to solve the multiplication of matrices E and D. This will help you understand the sequence of operations involved.

  4. Visualize the Multiplication

    Use graph paper or a digital tool to visually represent the multiplication of matrices E and D. Draw each matrix and use arrows to show how the rows and columns interact to form the resulting matrix. This activity will help you see the multiplication process in a new way.

  5. Matrix Multiplication Story

    Write a short story or comic strip that explains the process of multiplying matrices E and D. Use characters or objects to represent the rows and columns, and describe how they interact to create the resulting matrix. This creative activity will help solidify your understanding of matrix multiplication.

MatrixA rectangular array of numbers arranged in rows and columns. – In algebra, a matrix is often used to represent a system of linear equations.

MultiplicationThe mathematical operation of scaling one number by another. – Matrix multiplication involves taking the dot product of rows and columns.

ProductThe result of multiplying two or more numbers or expressions. – The product of two matrices is another matrix.

ValidLogically correct or acceptable within a given set of rules. – For matrix multiplication to be valid, the number of columns in the first matrix must equal the number of rows in the second matrix.

RowsHorizontal lines of elements in a matrix. – The matrix has three rows and four columns.

ColumnsVertical lines of elements in a matrix. – Each column in the matrix represents a different variable in the system of equations.

EntryAn individual element or number in a matrix. – The entry in the second row and third column of the matrix is 5.

DotA mathematical operation involving the sum of the products of corresponding entries. – To find the dot product of two vectors, multiply corresponding entries and sum the results.

CalculateTo determine the value of something through mathematical processes. – Calculate the determinant of the matrix to find its inverse.

ResultingOccurring as a consequence of a particular action or operation. – The resulting matrix from the multiplication is a 2×2 matrix.

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