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**Bgrasty** Not sure which method you have been using for finding A^{-1}, but if you think about the augmented 3x6 matrix with the last 3 columns as the Identity matrix (3x3 matrix with 1's down the diagonal), then doing GJ elimination on this matrix should yield a 3x6 matrix with the first 3 columns being the identity matrix and the last 3 columns now being A^{-1}. So to change {-1,-2,2} to {1,2,-2} you would multiply the whole first row {-1,-2,2,1,0,0} by -1 and get {1,2,-2,-1,0,0}. You can proceed through rows 2 and 3 the same way.