If a is a square matrix of order n and AAT = e, | a | = - 1, it is proved that | a + e | = 0, where e is the identity matrix

If a is a square matrix of order n and AAT = e, | a | = - 1, it is proved that | a + e | = 0, where e is the identity matrix

It is proved that ∵ a + e | = | a + AAT | = | a | - E + at | = - | (E + a) t | = - | - E + a | - 2 | - E + a | = 0, that is | - E + a | = 0