If A is a matrix, what does A' mean?
I have tried google this but nothing came up.
My new stats course had some review problems, and these multiple choice came up.
Which statement is true?
(a) (AB)' = A'B'
(b) (AB)' = B'A'
(c) Both a and b
(d) Neither a nor b
Which statement is true?
(a) A'' = A
(b) A''' = A'
(c) Both a and b
(d) Neither a nor b
$\endgroup$ 51 Answer
$\begingroup$As noted by others, it usually means the matrix transpose. This operation is an involutive anti-morphism, which is not the important thing to remember. The important thing is that:
$A''=A$, where $A''$ means $(A')'$, i.e., the transpose operation applied twice, see [Involution]
$(AB)' = B'A'$
Given this, it is not difficult to derive that the correct answers are (b) for the 1st question and (c) for the second one.
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