1.6 #T8
Given A^T = T and that A^-1 exists, show that (A^-1)^T = A^-1,
that is show that A inverse is symetric.

Proof: (A^-1)^T = (A^T)^-1 by Theorem 1.9(c).
       But A^T = A so (A^T)^-1 = A^-1. Thus,

             (A^-1)^T = A^-1.