I was just checking out some online bass lessons, and I realized that I don't fully understand the difference between some types of chords. The chords in question are: Dm7 G7 Cmaj7 A7 and sometimes it's written as A7(b9). My question is, what is the difference between a major, a 7, and a maj7 chord especially in relation to the chord tones (or arpeggios?) that are played? And what is the b9 about? How does that change a 7 chord? I already have some ideas about this stuff but there are some gaps in there too. Feel free to go into as much detail as you think is useful. Thanks for the help!