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# Which One is Idempotent?

LINALG-C4LBKC

Which of the following matrices is idempotent?

A

$\begin{pmatrix}1&1&0\\\ 0&1&0\\\ 0&0&0\end{pmatrix}$

B

$\begin{pmatrix}2&-2&-4\\\ -1&3&4\\\ 1&-2&-3\end{pmatrix}$

C

$\begin{pmatrix}0&0&1\\\ 0&1&0\\\ 1&0&0\end{pmatrix}$

D

$\begin{pmatrix}6&-2&4\\\ 0&1&0\\\ 2&0&-1\end{pmatrix}$