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I would like to understand how the following fact : detA⋅I n ⋅adj(adj(A))=(detA) n−1 ⋅A

allows us to determine/assert that if A isn't invertible then (adj(adj(A)) = 0.

If A isn't invertible I can't devide by detA.....

Thanks , Guy

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    I could understand all the proo$f$ but I don't understand $h$ow it helps to assert that i$f$ A isn't invertible t$h$en adj(adj(A)) = 0.2012-10-20

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As you already noted: This is not possible but it is not claimed in the link you provided.

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    let us [continue this discussion in chat](http://chat.stackexchange.com/rooms/6191/discussion-between-julian-kuelshammer-and-guy)2012-10-20