Major 7th chords are commonly used in place of plain major chords,the same goes for minor and dominant chords. The formula for Maj7 is ROOT-3-5-7, for Minor 7th chords are ROOT-b3-5-b7. In the key of F in the major scale this would be BE F-A-C-E. In the key of B# It's Bb-D-F-A. In the key of G this would be G-Bb-D-F. In the key of D It's D-F-A-C. Dominate 7th chords (7), sometimes referred to as "dominant," play a very important role in chord progressions, The formula for a 7 chord is Root-3-5-b7. It has a natural 3, like a major chord, and a b7 like a min7 chord. In the key of E it is spelled E-G#-B-D. In the key of A it's A-C#-E-G.
PRACTICE SPELLING Maj7, min7 and Dominant chords for the other tem keys. The attached song has examples of Maj 7th, min 7th and dominant 7th chords. First we'll start with the Cmaj7 chords;