question about matrix division (I'm getting division by 0?)  TOPIC_SOLVED

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question about matrix division (I'm getting division by 0?)

Postby lawrence on Fri Apr 03, 2009 6:24 pm

I have a question about matrix multiplication; well, actually, matrix division. I am assuming that matrices are divided the same as they are multiplied; that is, row by column. Specifically, the problem I am referring to:

[ 2  1 ] * A = [ 3  0 ]
[ 0 3 ] [-3 6 ]

To solve for A, would you divide the right matrix by the one on the left? If so, I come up with the following:

[ 3/2       3 ]
[-3/2+6/0 -1 ]

But what do I do with that 6/0?
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Re: question about matrix division (I'm getting division by 0?)  TOPIC_SOLVED

Postby Martingale on Fri Apr 03, 2009 6:51 pm

lawrence wrote:I have a question about matrix multiplication; well, actually, matrix division. I am assuming that matrices are divided the same as they are multiplied; that is, row by column. Specifically, the problem I am referring to:

[ 2  1 ] * A = [ 3  0 ]
[ 0 3 ] [-3 6 ]

To solve for A, would you divide the right matrix by the one on the left? If so, I come up with the following:

[ 3/2       3 ]
[-3/2+6/0 -1 ]

But what do I do with that 6/0?


you need to find the inverse matrix for

and multiply that to both sides
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Postby stapel_eliz on Fri Apr 03, 2009 7:10 pm

lawrence wrote:I have a question about matrix multiplication; well, actually, matrix division. I am assuming that matrices are divided the same as they are multiplied...

No; division is not defined for matrices. As the previous reply suggests, you have to use a different process. (I'm guessing you're self-studying or thinking ahead of your class syllabus...?)

With numbers, dividing by a value was the same as multiplying by the "multiplicative inverse", being the reciprocal of the intended divisor. For instance, 10 divided by 2 is the same as 10 times 1/2.

While matrices cannot be divided, they can (sometimes) have multiplicative inverses. To learn about this topic and the process for finding an inverse, try here. :wink:
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Re: question about matrix division (I'm getting division by 0?)

Postby lawrence on Sat Apr 04, 2009 11:30 am

Thank you both!
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