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If $A$ and $B$ are two conformable matrices,and $AB = A$ and $BA = B$ then prove that A and B are idempotent matrices.

This may be trivial but I am not sure how to proceed on this.

1 Answers 1

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$Ax = ABx = A(BA)x = (AB)Ax = AAx$

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    That's of course also fine2010-12-26