If anyone is wondering, this is the C6/9 chord shown on sheet music, a keyboard, and guitar tablature. I have started using the 6/9 chords a lot since they are just so warm and cozy.
A "6/9" chord means that when playing a triad (a chord with 3 notes), you would add the 6th and the 9th note in the scale that the chord is in. So for instance, the key of C has neither sharps nor flats, so C major is [C, D, E, F, G, A, B, C]. To make a C major triad, we take the 1st, 3rd, and 5th note of the series and play them together [C, E, G]. To make this a 6/9 chords, we add the 6th and 9th, so [C, E, G, A, and D].
The sequence in the major scale I provided has only 8 notes in it, so to make a note the 9th, you are just taking the 2nd and popping it up an octave. In this case, D is both the 2nd and 9th, but we say the 9th because we want to have that D on the high end of the note and really sing out!
Fair! C9 does imply the 7th, but I always thought the 6 in C6/9 was over ruling the 7th.
I actually never thought about the difference between 9 and (add 9)- thank you for that!