Answer:
The correct matrices are:
Matrix:
7 1 5
1 5 7
5 7 1
all diagonal elements of A^2 are: 7^2 + 1^2 + 5^2
Matrix:
9 18 27
27 -9 18
18 27 9
all diagonal elements of A^2 are: 9^2 + 27*18 + 18*27 or (-9)^2
Matrix:
8 1 6
6 8 1
1 6 8
all diagonal elements of A^2 are: 8^2 + 6*1 + 1*6
