Question 1044262
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1. if A is a square matrix. What is meant by A is {{{highlight(cross(indepontent))}}} idempotent, nilpotent and involutory 
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1. An idempotent matrix.  See <A HREF=https://en.wikipedia.org/wiki/Idempotent_matrix>this</A> Wikipedia article.

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    In algebra, an idempotent matrix is a matrix which, when multiplied by itself, yields itself. 
    That is, the matrix M is idempotent if and only if MM = M. For this product MM to be defined, M must necessarily be a square matrix. 
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2, 3.  nilpotent and involutory

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See corresponding Wikipedia articles found by GOOGLE, for example.
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Wikipedia, GOOGLE and Internet are your friends and colossal source of information.