Using aned one-liner:
printf "%s\n" '?^OPERATIONAL SYSTEMS TOMORROW:$?,$w' | ed -s arquivo
or with ex instead:
ex -sc '?^OPERATIONAL SYSTEMS TOMORROW:$?,$wq!' input.txt
these rewrite arquivo to save only everything from the last matching line to the end of the file.
Using a file-oriented tool like ed or ex instead of a stream-oriented one like sed or awk makes many non-trivial automated editing tasks much simpler because they can do things like search backwards from a cursor location.