I was reading this book and it says

determine a real invertible matrix P such that P^TAP is diagonal

where

matrix A is

$\displaystyle [(0 , 1 , 2), (1 , 0 , 0 ),(2 , 0 , 0)]$

I want to know how to find P.

The text book skipped the steps that i want.

I want to know the steps.

Thank you