Which of the following matrices is idempotent (i.e., A2=AA^2 = AA2=A)?
(1100)\begin{pmatrix} 1 & 1 \\ 0 & 0 \end{pmatrix}(1010)
(0110)\begin{pmatrix} 0 & 1 \\ 1 & 0 \end{pmatrix}(0110)
(100−1)\begin{pmatrix} 1 & 0 \\ 0 & -1 \end{pmatrix}(100−1)
(2002)\begin{pmatrix} 2 & 0 \\ 0 & 2 \end{pmatrix}(2002)