Question 921460
Explaining synthetic division is more difficult than actually performing it.


Here is a text-based arrangement 


________-6______|________2_____-9______-16________12
________________|
________________|
__________________________________________________________



Follow the process, as example at least:


________-6______|________2_____-9______-16________12
________________|
________________|_____________-12______126______-660
__________________________________________________________

________________________2_____-21______110_______-648



The remainder  {{{-648<>0}}};
Negative 6 is not a root.