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David Hand's avatar

Since Martin gave both the matrix and its inverse, my guess is that, rather than calculating the inverse from scratch, Emilio simply multiplied the two matrices together to see if it produced the identity. Thus 1x(-24) + 2x20 +3x(-5) = 1 as it should, but 0x18 + 1x15 + 4x4 is not 1. But replace the 15 by -15 and it is 1. Still very impressive, as he has to do this for all 9 entries, and to notice that a simple change of sign will do it.

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Terry M Morin's avatar

thank you for this article. it so reminds of me of what the psalmist says in Psalm 139, '.. "for I am fearfully and wonderfully made"

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