I have been trying to understand this solution and I can not wrap my head around the fact that $a_{11}$ = $a_{22}$ = 0. What is this conclusion based on? Is it due to the fact that they are related by A and its transpose $A^T$?
Can not imbed the picture due to this being my first post: https://i.stack.imgur.com/Nr6G7.jpg
It is because $a=-a \iff a=0$.