1234567
of 7

Multiplying Matrices

YOUR TURN:

A = [ row 1: 11 , 6 row 2: -3 , -7 ]

B = [ row 1: -5 , 4 row 2: 1 , -8 ]

Find  A times B.

Now find  B times A (and don't just assume you'll get the same thing as you did for  A times B !)

You got two totally different things, didn't you?

A times B = [ row 1: -49 , -4 row 2: 8 , 44 ]

B times A = [ row 1: -67 , -58 row 2: 35 , 62 ]


( A times B ) does not equal ( B times A )

So, matrix multiplication is NOT commutative!

(Well, most of the time, anyway.)

TRY THIS:
(It's a bit of a review, too!)

A = [ row 1: 1 , 6 row 2: -4 , 9 ]               B = [ row 1: 8 , 3 row 2: -2 , -7 ]

C = [ row 1: 10 , 1 row 2: -5 , 0 ]
 

Find  2A + BC + 3BA .

*hint: Do the matrix multiplications first,
then put everything together slowly.