Which of the following matrices is orthogonal (satisfies AAT=IAA^T = IAAT=I)?
12(1111)\frac{1}{2}\begin{pmatrix} 1 & 1 \\ 1 & 1 \end{pmatrix}21(1111)
12(11−11)\frac{1}{\sqrt{2}}\begin{pmatrix} 1 & 1 \\ -1 & 1 \end{pmatrix}21(1−111)
(2002)\begin{pmatrix} 2 & 0 \\ 0 & 2 \end{pmatrix}(2002)
(1234)\begin{pmatrix} 1 & 2 \\ 3 & 4 \end{pmatrix}(1324)