1. The problem statement, all variables and given/known data If the entries of A and A^-1 are all integers, how do you know that both determinants are 1 or -1? 2. Relevant equations 3. The attempt at a solution I know that 1 = det I = detAA-1=detA * detA-1= detA*(1/detA) = 1 Not sure how we get to - or the role integers play in it. Thanks for your help!