Which matrix represents a rotation of 180∘180^\circ180∘?
(1001)\begin{pmatrix} 1 & 0 \\ 0 & 1 \end{pmatrix}(1001)
(−100−1)\begin{pmatrix} -1 & 0 \\ 0 & -1 \end{pmatrix}(−100−1)
(0−110)\begin{pmatrix} 0 & -1 \\ 1 & 0 \end{pmatrix}(01−10)
(01−10)\begin{pmatrix} 0 & 1 \\ -1 & 0 \end{pmatrix}(0−110)