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Linear AlgebraChallengeDeterminants & Inverses

Determinants & Inverses · Challenge problem

A 3×33\times3 matrix AA has positive determinant and adjugate adj⁡A=(3−6213−1−121)\operatorname{adj}A = \begin{pmatrix}3 & -6 & 2\\1 & 3 & -1\\-1 & 2 & 1\end{pmatrix}. Find the sum of all nine entries of AA.