One very interesting thing to know is that a minor 9 arpeggio contains a major 7 arpeggio. Indeed, the superimposition of two seventh arpeggios (minor and major seventh) gives a minor 9th arpeggio.

Minor 9th arpeggio 1 b3 5 b7 9 Minor 7 arpeggio 1 b3 5 b7 X Major 7 arpeggio X b3 5 b7 9

Let's take an example with the C minor 9 arpeggio. It is built with C (root), Eb (minor third), G (fifth), Bb (minor seventh) and D (ninth). You find out that when starting on the minor third (Eb) of C min you obtain an Eb major 7 arpeggio made up of the minor third (Eb), the fifth (G), the minor seventh (Bb) and the ninth (D) of Cmin9. Playing an Ebmaj7 arpeggio over a Cmin7 chord gives a Cmin9.

