Math 11 Matrix Multiplication and Determinant

Matrix Operations

What if I told you the world you know is not real?... Anyway, here's some math

​What is a Matrix?

​A matrix is a block of numbers which includes multiple distinct values. Matrices (the plural of "matrix") have dimensions which are written as the number of rows x the number of columns. Each number within a matrix is called a "term" of that matrix. "Corresponding terms" are terms in different matrices that are in the same location in their respective matrices.

​Adding Matrices

​We can perform operations with matrices. To add two matrices, you add corresponding terms to each other. Subtraction works exactly the same way except you subtract the corresponding terms instead of adding them.

​Note!

Some matrices cannot be added or subtracted. If the matrices do not have the same dimensions, then they cannot be added to each other.​ The top matrices cannot be added since they have different dimensions. The bottom matrices can be added since they have the same dimensions.

​Multiplying by a Scalar

​When we multiply a matrix by a scalar, we multiply each term by the scalar outside the matrix. In the example to the right, we multiply each term in the matrix by 2.

Multiple Choice

In Matrix R (pictured) what element is in the second row, third column?

• 8
• 9.01
• 6
• 1

Multiple Choice

What must be true in order to ADD two matrices?

• They must be square.
• The dimensions must be equal.
• The determinant can't equal 0.
• The column of the 1st must equal the row of the 2nd.

Multiple Choice

What are the dimensions of this matrix?

• 2 x 3
• 3 x 2
• 6 x 1
• 1 x 6

Multiple Choice

Multiply

• 20     15    -10
  30     -5         0
• -20      15     -10
  30     -5          0
• 1        8       3
  11     4        5
• 20     -15     10
  -30         5        0  

Multiple Choice

Find B-A

• -3     1
  7     -1
• 1     0
  1     -4
• 4       0
  -6     0
• not possible because rows do not match columns

​Multiplying Matrices

​Multiplying matrices takes more time and steps. First, we have to make sure that we can multiply the two matrices we want to multiply. We have to compare the number of columns in the first matrix to the number of rows in the second matrix. If they match, then we can multiply the matrices. If they do not, then we cannot multiply them and there is no solution.

​Multiplying Matrices

​The product matrix will have the number of rows from the first multiple and the number of columns from the second multiple. This helps us make sure we are multiplying correctly.

​Multiplying Matrices

Once we know we can multiply matrices, then we can start the process. First, highlight the first row in the first matrix and the first column in the second matrix. Multiply the first terms, then the second terms, and then the third terms, and so on. Add the products of each multiplication and that is the first term in the product matrix.

​Multiplying Matrices

After the first term is found, using the first row from the first matrix, do the same operation using the second column in the second matrix. The resulting term is in the first row, second column of the product matrix. Continue this process using the first row until there are no more columns left. Then, repeat the process using the next row.

Multiple Choice

You can multiply a 2X3 matrix by which matrix?

• 2X2
• 2X12
• 3X12
• 2X3

Multiple Choice

When a 3x6 matrix is multiplied by a 6x5 matrix, what will the dimensions of the product be?

• 6x6
• 3x6
• 3x5
• 5x6

Multiple Choice

If the matrices can be multiplied, what are the dimensions of the product?

• Matrix multiplication is not possible.

• 3 x 1

• 1 x 2

• 3 x 2

Multiple Choice

Find the product.

• Not possible.

• -3 16

  17 12

  8 -10

• 3 12

  -15 -8

  -1 -3

Multiple Choice

Find the product.

• No Product Exists

Multiple Choice

Find the product of the matrices.

• A
• B
• C
• D

Multiple Choice

Find the product of the two matrices.

• 17 12

  25 18

• 17 12

  12 6

• 17 12

  7 5

• 17 12

  10 12

Multiple Choice

These matrices are being multiplied. Determine the dimension/size of the new matrix. 

• Can't multiply them

• 4  x  2

• 3  x  3

• 4  x  3

Determinants

Multiple Choice

Find the determinant of the following matrix.

• -12

• -10

• 12

• 10

Multiple Choice

Find the determinant of the following matrix.

• -7

• 7

• -23

• 23

Multiple Choice

Find the determinant of the following matrix.

• 8

• -8

• 18

• -18

Poll

One gotta go

Multiple Choice

What is the formula for the determinant of a 2x2 matrix?

• ad-bc

• ab-cd

• ad+bc

• (a+d)(b+c)

Multiple Choice

What is the determinant of this matrix?

• 0

• 24

• -24

• -12

Multiple Choice

Evaluate the determinant of the matrix.

• -21
• 0
• 9
• 12