Which of the following matrices are orthogonal?
(cosθ−sinθsinθcosθ)\begin{pmatrix} \cos \theta & -\sin \theta \\ \sin \theta & \cos \theta \end{pmatrix}(cosθsinθ−sinθcosθ)
(1101)\begin{pmatrix} 1 & 1 \\ 0 & 1 \end{pmatrix}(1011)
12(111−1)\frac{1}{\sqrt{2}} \begin{pmatrix} 1 & 1 \\ 1 & -1 \end{pmatrix}21(111−1)
(0220)\begin{pmatrix} 0 & 2 \\ 2 & 0 \end{pmatrix}(0220)