A major guitar chord
A major guitar chord(or the key of A) is a major scale based on A, with the pitches A, B, C♯, D, E, F♯, and G♯. Its key signature has three sharps.
Its relative minor is F-sharp minor and its parallel minor is A minor. The key of A-major is the only key where a Neapolitan sixth chord on 
requires both a flat and a natural accidental.
Although not as rare in the symphonic literature as sharper keys, examples of symphonies in A major guitar chords are not as numerous as for D major or G major. Beethoven's Symphony No. 7, Bruckner's Symphony No. 6 and Mendelssohn's Symphony No. 4 comprise a nearly complete list of symphonies in this key in the Romantic era. Mozart's Clarinet Concerto and Clarinet Quintet are both in A major, and generally Mozart was more likely to use clarinets in A major than in any other key besides E-flat major.[1]