Linear Algebra orthogonal matrix

[kidia]

I need help on this one,Given the symmetric matrix A=
|0 2 2|
|2 0 2|
|2 2 0|

Find an orthogonal matrix P so that PAP^-1 is a diagonal matrix.

[Unco]

Find the eigenvalues and eigenvectors of A. The columns of P are the eigenvectors.