[adwight]

I totally forget how to multiply matrices, and I have a final tomorrow, and half the test is on it.  Can you help me???  Just walkthrough a problem, like this:

[-2 1]    [4 2]
[3 0]  x  [-1 6]

I can't remember how to multiply those matrices.  (They're 2x2 btw, the one on the left and the other on the right.)  Thank you!!!

[Petrarch of the VBB]

You haven't posted since Christmas Eve, and you expect us to help you?!? HAH!

I would help, but I haven't a clue.

[adwight]

Bah, shut up... I have too, just not in this forum.  I've been too busy, but I'm coming around.  Please someone help me!!!(I'm desperate, I don't want to fail.)

[Petrarch of the VBB]

Nobody wants to fail, but these things happen.

Anyway, where's CP when you need him?

[Goober5000]

Half the test is on just matrix multiplication?

Anyway, here's how...

Code: [Select]

[ a  b ] x [ e f ]
[ c  d ]   [ g h ]

equals

[ ae + bg   af + bh ]
[ ce + dg   cf + dh ]

[Joey_21]

Hmm.... believe it or not, I've not once ever gone over matrices in any of my mathematics classes.

[Petrarch of the VBB]

See! They never teach you anything even remotely useful.

[Kamikaze]

Originally posted by Joey_21
Hmm.... believe it or not, I've not once ever gone over matrices in any of my mathematics classes.

pretty much same here, they don't teach us proper linear algebra 'til college. I just learn it on my own

[CP5670]

They did some basics of the matrix multiplication stuff in precalculus for me. That course was kind of weird, as they do a little bit of stuff from several topics without going into any of the topics in depth.

as for the original question, in general if AB=C (A is an i´m matrix and B is an m´j one), then C is an i´j matrix with elements C_ij = å_k=1^m-1A_ikB_kj where the A_ij thing means the element in the i-th row and j-th column.

[CP5670]

hmm my post got cut off in the middle for some reason and it won't let me edit it...

[Goober5000]

So post again.

[adwight]

So, what's the answer geniuses... jk

[Razor]

as for the original question, in general if AB=C (A is an i´m matrix and B is an m´j one), then C is an i´j matrix with elements Cij = åk=1m-1AikBkj where the Aij thing means the element in the i-th row and j-th column.

Pass the bazooka.

__________________________________________________
[-2 1] [4 2]
[3 0] x [-1 6]

__________________________________________________

The first one's answer is: [-8 ,  2]

The second one: The answer is 18, I think. That x is not for multiplication, it is read as ordinary x and that operation is waaay different from the first one.

[Sandwich]

Originally posted by Goober5000
...matrix multiplication...

They're coming....!

[kode]

Originally posted by Razor


Pass the bazooka.

__________________________________________________
[-2 1] [4 2]
[3 0] x [-1 6]

__________________________________________________

The first one's answer is: [-8 ,  2]

The second one: The answer is 18, I think. That x is not for multiplication, it is read as ordinary x and that operation is waaay different from the first one.

you're on drugs, aren't you?

goober5k already provided the method for calculating it.

[Razor]

Originally posted by kode


you're on drugs, aren't you?

From Kode's signature: I'm a glue addict.

Really? Look who's talking By the way, check this out

[kode]

Originally posted by Razor


Really? By the way, check this out

umm, yeah. that's really mature.

I just wish I had flash so it worked, dumbwit.

[Razor]

umm, yeah. that's really mature.

[Tiara]

Whats so funny about a moving "You are an idiot" window? You just close it and its gone. Now if there would be a popup bomb behind it, it might be fun to get people you dislike to click it

[Razor]

Originally posted by Tiara
Whats so funny about a moving "You are an idiot" window? You just close it and its gone. Now if there would be a popup bomb behind it, it might be fun to get people you dislike to click it

That's exactly the point. It's a multiplying bomb.