After entering the first door, you find yourself in a bigger room. You look at the keypad.
[+] [-] [X] [÷] [∞] [±] [ENTER]
You look around the room. Then, you see the paper.
And, as before, there is a hint carved into the wall -
A to Z Alphabet
This time, the answer seems to be a maths symbol. Or symbols. Still, you've got this far, so you may as well try.
There is only one symbol involved.
A to Z was not required. It could have been A to B, I to C or anything. Each one changes the encrypted text. Now, which cipher is that?
It is an eight-letter word.
AAAABABAAAAABABABAAAAAABB I love bacon.
The cipher used above is called Baconian.
The next door will be added when the current door is solved!