Hey J,
Let me answer your questions
1. What do you mean by 17? I though there were only 8 degrees to a scale.
Sorry for not being clearn here. I was talking about scale degrees I (one) and I7 (one seven) in the key of C that would be C to C7 or C major to the C dominant 7
2. Why are you playing both the root and the 7th in the left hand? I understad why you would play the 7th as your playing the third inversion of the chord.
One thing you need to remember is "A chord is a chord is a chord"
As long as the tones that are need to make that chord is present, it is that chord. Example
Hit the middle c, then hit the G above that, and the E above that (C G E) ??? What chord is that?? Its a C chord Inversions are import but also knowing what notes make up certain chords is important also
For this Example:
C / C E G
C Bb / C E G
I played the Bb in the left hand to change the chord from a C to a C7 chord. Remember, as long as the notes are present it can be that chord.
Im confused, how can that be an A chord? It looks like a Cmaj triad with an A base note?
C / C E G
A / C E G
Remember to not just look at one hand, look at the entire chord being played. The notes A C E G make up the Am (A minor) chord (in the context of the the key of C).
You are askling the same question I use to ask. If you still don't understand, keep asking. Thats the ony way you are going to get it.