MHB Adj ( adj A ) = ( det A )^(n-2) A (ARSLAN's question at Yahoo Answers)

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The discussion centers on proving the equation adj(adj(A)) = A(det A)^(n-2) for an n x n matrix A. It references the relationship between an invertible matrix M and its adjugate, stating that adj M can be expressed in terms of M's determinant and its inverse. By applying properties of determinants and adjugates, the proof derives that the adjugate of the adjugate of A simplifies to the product of A and the determinant raised to the power of (n-2). The mathematical steps provided clarify how these properties lead to the final result. This proof reinforces the foundational concepts of linear algebra regarding matrix adjugates and determinants.
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Hello ARSLAN,

If $M$ is an invertible $n\times n$ matrix, then $M^{-1}=\dfrac{1}{\det M}\mbox{adj } M$ that is $\mbox{adj } M=(\det M)M^{-1}$.

Using well known properties ($\det (aM)=a^n\det M$, $(aM)^{-1}=a^{-1}M^{-1}$ etc):
$$\mbox{adj } \left(\mbox{adj }A \right)=\mbox{adj } \left((\det A)A^{-1}\right)=\det\left((\det A)A^{-1}\right)\cdot\left((\det A)A^{-1}\right)^{-1}\\\left((\det A)^n\cdot\frac{1}{\det A}\right)\cdot\left(\frac{1}{\det A}\cdot (A^{-1})^{-1}\right)=(\det A)^{n-2}A$$
 
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