1. Warm-Up 4 minutes Give the dimensions of each matrix. 1) 2)
Identify the entry at each location of the matrix below.
3) b12
4) b21
5) b ) 3

2. 4.2 Matrix Multiplication
Objectives:
Multiply two matrices
Use matrix multiplication to solve mathematical and real-world problems

3. Matrix Multiplication
A football team scores 5 touchdowns, 4 extra points, and 2 field goals. A touchdown is worth 6 points, an extra point is worth 1 point, and a field goal is worth 3 points. The final score is:
(5 touchdowns)(6 pts)
+ (4 extra points)(1 pt)
+ (2 field goals)(3 pts)
= points
points
points
= points
touch-
downs
extra
points
field
goals
point
values
total
score 6 5 4 2 1
(5)(6) +
(4)(1) +
(2)(3) 3

4. Matrix Multiplication
To multiply any two matrices, the inner dimensions must be the same.
Then the outer dimensions become the dimensions of the resulting matrix.
inner dimensions
product dimensions
2 x 3
3 x 4
= 2 x 4
outer dimensions

5. Example 1 Find the product. 1 x 3 3 x 2 = 1 x 2 (2)(8) + (5)(0) +
(0)(2)
(2)(1) +
(5)(4) +
(0)(5)

6. Practice
Let A =
and B =
Find AB and BA.

7. Homework
p.229 #7-19 odds,25