|-2（A^T B^-1)^-1|=(-2)^3 |(A^T B^-1)^-1|= -8 |(A^T B^-1)|^-1= -8 |A^T|^-1 |B^-1|^-1= -8 |A|^-1 |B|= -8 x (1/2) x 3= -12.
