enharmonic = a different letter name for the same key
C flat.
b
A double sharp is the enharmonic of B nature
"Flat" means to go down one semitone. Look at a piano (or similar) keyboard, and check what you have one to the left of "C". Since on a piano there is no black key between "B" and "C", the next semitone down from "C" is simply "B".
E natural
There are two definitions of the phrase "enharmonic equivalent", referring to the enharmonic equivalent of a single note, or the enharmonic equivalent of a key, or key signature.In the first instance, the enharmonic equivalent of the note E flat is D sharp (D#). The enharmonic equivalent of the key signature E flat major is D sharp (D#) major.
b
A double sharp is the enharmonic of B nature
It is the same thing as playing a B natural because on an enharmonic scale that is how it goes.
"Flat" means to go down one semitone. Look at a piano (or similar) keyboard, and check what you have one to the left of "C". Since on a piano there is no black key between "B" and "C", the next semitone down from "C" is simply "B".
b
A sharp.
B flat
A sharp
The enharmonic of E-sharp is F-natural.
B flat
Yes, B sharp does exist in music theory. It is the enharmonic equivalent of C natural, meaning that they are the same pitch but spelled differently.
E natural