Composers rarely do works in this key. Sonata in F#, Opus 78 is by Beethoven. Impromptu in F# is a work by Chopin in the same key.
E-sharp.
The key that includes both F sharp and C sharp is the key of D major.
In the key of D major, the notes that are sharp are F, C, and G.
One sharp could be G major or E minor.
The key signature of D sharp major has nine sharps: F, C, G, D, A, E, B, and F.
G major, D major, E major, B major, F sharp major, F sharp minor, A sharp major, etc.
F sharp.
what is the relative minor of f sharp major
The key of Gmajor has 1 sharp which is F sharp.
The key of G Major has one sharp: F#
There are six sharps in F sharp major.
f sharp
The mediant of any major scale is the note that is a third above the tonic (root) of the scale. In the key of F sharp major, the tonic is F sharp, so the mediant would be A sharp.
That would be either A major or F# minor.
F# major. f sharp, c sharp, g sharp, d sharp, a sharp, e sharp
A major, or F# minor
The key with three sharps is A major, however A major uses C sharp - alongside with G sharp and F sharp - instead of D sharp.