Monday, 1 August 2016

linear algebra - Intuition behind Matrix being invertible iff determinant is non-zero

I have been wondering about this question since I was in school. How can one number tell so much about the whole matrix being invertible or not?



I know the proof of this statement now. But I would like to know the intuition behind this result and why this result is actually true.






The proof I have in mind is:



If A is invertible, then




1=det(I)=det(AA1)=det(A)det(A1)



whence det(A)0.



Conversely, if det(A)0, we have



Aadj(A)=adj(A)A=det(A)I



whence A is invertible.




adj(A) is the adjugate matrix of A.



adj(A)ji=(1)i+jdet(Aij)



where Aij is the matrix obtained from A by deleting ith row and jth column.



Any other insightful proofs are also welcome.

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