Wiskunde Multiple Choice Vraag uit Gricha's Wiskundige Vragenbank

Which matrix is NOT idempotent ?
A	B	C	D	E
$https://latex.codecogs.com/png.image?\dpi{110}\begin{bmatrix}1 & 0 \\0 & 1 \\\end{bmatrix}$	$https://latex.codecogs.com/png.image?\dpi{110}\begin{bmatrix}0 & 1 \\1 & 0 \\\end{bmatrix}$	$https://latex.codecogs.com/png.image?\dpi{110}\fn_jvn&space;\begin{bmatrix}0 & 0 \\0 & 0 \\\end{bmatrix}$	$https://latex.codecogs.com/png.image?\dpi{110}\begin{bmatrix}1 & 0 \\0 & 0 \\\end{bmatrix}$	$https://latex.codecogs.com/png.image?\dpi{110}\begin{bmatrix}2 & 1 \\-2 & -1 \\\end{bmatrix}$

$https://latex.codecogs.com/png.image?\dpi{110}De\;tweede\;want\\\\\begin{bmatrix}0&1\\1 &0\\\end{bmatrix}\cdot \begin{bmatrix}0&1\\1 &0\\\end{bmatrix}=\begin{bmatrix}1&...\\... &...\\\end{bmatrix}$