Math Is Fun Forum

mom

Member

Registered: 2012-04-25

Posts: 94

Just want to make sure I am doing this correctly

I have:
Let A=[-2 1 3] and B = [0 1 -3]. Find the second row of AB.
            1 0 5                1 3 -4
            0 4 2                3 0  1

I multiplied and for the second row of AB, I got [15 1 2]

Is this correct?

{7/3}

Member

Registered: 2013-02-11

Posts: 210

Re: Just want to make sure I am doing this correctly

I'm confused,how can 1 by 3 and 1 by 3 matrices be multiplied?

---

There are 10 kinds of people in the world,people who understand binary and people who don't.

Bob

Administrator

Registered: 2010-06-20

Posts: 10,621

Re: Just want to make sure I am doing this correctly

hi mom,

That's correct.

{7/3} :  I think those are two 3 x 3 matrices.

Bob

---

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

mom

Member

Registered: 2012-04-25

Posts: 94

Re: Just want to make sure I am doing this correctly

Please see attached. I have never uploaded in here before but the attachment shows how I did my work.

I know how to go through the process of multiplication for the matrices. I am just not sure that is what the question was asking me to do.

mom

Member

Registered: 2012-04-25

Posts: 94

Re: Just want to make sure I am doing this correctly

Bob,

yes they are two 3 x 3 matrices. So for the second row of AB it would be [15 1 2] ?

It didn't say to multiply so I wasn't sure that I worked the problem correctly but if you have A matrix B matrix and you have to come up with the second row of AB for the matrices, was I correct in assuming that I was to multiply?

Thanks so much.

Bob

Administrator

Registered: 2010-06-20

Posts: 10,621

Re: Just want to make sure I am doing this correctly

Yes; in matrix work AB means A multiplied by B.

Bob

---

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

mom

Member

Registered: 2012-04-25

Posts: 94

Re: Just want to make sure I am doing this correctly

Bob,

thanks so much.