Problem on Matrices (Linear Algebra)

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If A is a real orthogonal matrix and $I+A$ is non singular prove that the matrix $(I+A)^{-1}(I-A)$ is skew symetric

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We put $M= (I+A)^{-1}(I-A)$.

We have $(I+A)(I-A^T)=I-AA^T+A-A^T=A-A^T$ because $A$ is orthogonal.

So $(I-A^T)=(I+A)^{-1}(A-A^T)$

And from $(I-A)(I+A^T)=-A+A^T$, we obtain $(A-A^T)(I+A^T)^{-1}=-(I-A)$

So $ M^T=(I-A^T)(I+A^T)^{-1}=(I+A)^{-1}(A-A^T)(I+A^T)^{-1}=-(I+A)^{-1}(I-A)=-M$