Show for a square matrix, the followings are equivalent.
The columns of A are all vectors of length 1, and are all at right angles to each other.
A^T = A^−1
Check whether or not the matrix A=[1 1 1
0 - 2 2
0 - 2 - 3] is diagonalisable. If it is, find a matrix P, and a matrix D such that P^-1 AP=D. If A is not diagonalisable find AdjkA).