Just to add a bit: in my country blinking your emergency lights (when all of your turn signals are going) for 2-3 times as a thank you is very common. It's even considered rude not to use them e.g. after you were let in.
I don't know if that is something in other countries. I live in Hungary.
It's so strange that it was always taught me as a²+b²+2ab. Of course I know it doesn't matter, but still strange to see it this way.