Blues typically follows a 12 bar pattern based around Dominant 7th Chords:
||: A7 | D7 | A7 | A7 | D7 | D7 | A7 | A7 | E7 | D7 | A7 | E7 :||
We've look at many different ways of playing dominant 7th chords on the guitar before, but we can make the blues progressions more interesting to play and listen to by using extended chords.
9th chords use these degrees of the major scale: 1, 3, 5, b7, 9
A9 uses the notes: A, C#, E, G, B
Try playing through the above blues chord progression with 9th chords and tune in tomorrow for another guitar chord of the day.