Is Matrix Multiplication Commutative?

[Peter G.]

Hi

I don't really know how to post a matrix here so I will try and make it as clear as possible.

Matrix A: 4 -1
2 3

Matrix B: 6 4
-5 -3

Matrix C: 1 2
3 4

We are given that APB = C and we are asked for P

What I did was I multiplied both sides by the inverse of (A*B), hence:

P = (A*B)^-1 * C

I got a different answer than the book however, could anyone check?

My answer:
1.85 1.95
2.85 2.95

Book:

1.6 1.8
2.9 3.2

Thanks,
Peter G.

 

[SammyS]

Hi

I don't really know how to post a matrix here so I will try and make it as clear as possible.

Matrix A: 4 -1
2 3

Matrix B: 6 4
-5 -3

Matrix C: 1 2
3 4

We are given that APB = C and we are asked for P

What I did was I multiplied both sides by the inverse of (A*B), hence:

P = (A*B)^-1 * C

I got a different answer than the book however, could anyone check?

My answer:
1.85 1.95
2.85 2.95

Book:

1.6 1.8
2.9 3.2

Thanks,
Peter G.

Hi Peter,

Matrix multiplication is not commutative!

Multiply on the left by A^-1 and on the right by B^-1.