2. Section 4.2 – Multiplying Matrices Day 2
Algebra 2 Unit 3 – Chapter 4
Section 4.2 – Multiplying Matrices
Day 2

3. MATRICES
ROWS
NAME
COLUMNS

4. MATRICES
Labeling Elements

5. MATRIX MULTIPLICATION
The order in which you list the matrices does matter. The column dimension of the first matrix must equal the row dimension of the second matrix. The row dimension of the first matrix and column dimension of the second matrix determine the size of the product matrix.

6. MATRIX MULTIPLICATION
State the dimensions of each matrix.
Can we multiply A x B? Can we multiply B x A?
2 x 2
2 x 3
YES NO

7. MATRIX MULTIPLICATION
You always multiply a row by a column. The result will be a new element.
Our result of 16 will be new element c11, because it was a combination of row 1 and column 1 of our two matrices that are being multiplied together.

8. MATRIX MULTIPLICATION
You always multiply a row by a column. The result will be a new element.
Our result of 26 will be new element c21, because it was a combination of row 2 and column 1 of our two matrices that are being multiplied together.

9. MATRIX MULTIPLICATION
To finish the problem, repeat the process multiplying row 1 and 2 of matrix A, with rows 2 and 3 of matrix B.
Element c12 = 3●6 + 2●3 = 24
Element c13 = 3●7 + 2●8 = 37
Element c22 = 4●6 + 5●3 = 39
Element c23 = 4●7 + 5●8 = 68

10. MATRIX MULTIPLICATION
Finish the problem by placing the final product’s elements into their correct location.

11. MATRIX MULTIPLICATION
BLOCK METHOD
MULTIPLY
MULTIPLY 37

12. MATRIX MULTIPLICATION
BLOCK METHOD
MULTIPLY
MULTIPLY 37 21

13. MATRIX MULTIPLICATION
BLOCK METHOD
MULTIPLY
MULTIPLY 37 21 2

14. MATRIX MULTIPLICATION
BLOCK METHOD
MULTIPLY
MULTIPLY 37 21 2
-14

15. MATRIX MULTIPLICATION
BLOCK METHOD 37 21 2
-14

16. GUIDED PRACTICE
1. Find AB if A =
and B = –
1 –2
–3 –2
ANSWER
– –21

17. GUIDED PRACTICE
Using the given matrices, evaluate the expression.
A = – –
, B =
–2 –1
, C = –
2. A(B – C)
3. AB – AC
(AB) –1 2
ANSWER
ANSWER
ANSWER
–5 –3.5 – –
–13 – –
–13

18. Multiplying Matrices Practice #1
PARTNER PRACTICE
Multiplying Matrices
Practice #1

19. HOMEWORK
Page 211 – 212
#11 – 33 ODD