Then, \( a^2 = 1 \) and \( d^2 = 1 \). So, \( a = \pm 1 \) and \( d = \pm 1 \). The diagonal matrices \( eginpmatrix \pm 1 & 0 \ 0 & \pm 1 \endpmatrix \) satisfy \( T^2 = I \). - Abu Waleed Tea