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Suppose that: E_4 [[1,3,4],[2,2,3],[-5,4,4]] = [[1,3,4],[8,8,12],[-5,4,4]] Find E_4 and...

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chocobob | Student | (Level 2) Honors

Posted April 23, 2013 at 9:47 PM via web

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Suppose that:

E_4 [[1,3,4],[2,2,3],[-5,4,4]] = [[1,3,4],[8,8,12],[-5,4,4]]

Find E_4 and (E_4)^-1

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mathsworkmusic | (Level 1) Educator

Posted May 29, 2013 at 10:34 AM (Answer #1)

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`E_4` is an elementary matrix. That is, one that can be reached from the identity matrix of the same dimension by an elementary operation.

In this case the operation is multiplying row 2 by 4.

Therefore `E_4 = ((1,0,0),(0,4,0),(0,0,1))`

`E_4^(-1)`  is also an elementary matrix and is simply the inverse operation, ie dividing row 2 by 4. So that

`E_4^(-1) = ((1,0,0),(0,1/4,0),(0,0,1))`

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