12.1 Adding and Subtracting Matrices

How many rows are in a 7 × 3 matrix?

• 7

• 3

• 21

• 10

How many columns are in a 5 × 4 matrix?

• 5

• 4

• 20

• 9

What are the dimensions of this matrix?

• 2 × 3

• 3 × 2

• 6 × 1

• 1 × 6

What must be true in order to add or subtract two matrices?

• They must be square

• They must have the same dimensions

• The discriminant can't equal 0.

• The columns of the first must equal the rows of the second

Find A + B:

• 8     10

  8      1 

• 12     25

  7     1

• 10     30

  0     1

• Not possible

Find B – A:

• –4     0

  6      –1

• 4     0

  –6     1

• 12     25

  7     0

• Not possible

Add:

• 11    8

  -4     2

• 3     2

  -6    -6

• -3    2

  -4    -6

• 10    8

  -6    2

Subtract:

• -5

  -8

  3

  10

• -9

  8

  3

  2

• -9

  -8

  3

  2

• -5

  8

  3

  2

Subtract:

• 3    -8

  0   -1

• 3   -4

  8  -13

• -3   8

  0    1

• 3   -8

  -8    1

Add:

• -2   4   -9

  -1   -6   -17

• -8   12   -9

  1   6   17

• -8   4   -9

  15   6   7

• -2   -4   -9

  15   6    7