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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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