C6/9 chord for piano with keyboard diagram.
Explanation: The C sixth/ninth is a five-note chord. Due to practical circumstances, however, the fifth (G) is often omitted and/or the chord is played inverted. The chord is abbreviated C6/9. It can also be written C6add9 or Cmaj6add9.
Theory: The C6/9 chord is constructed with a root, a major third, a perfect fifth, a major sixth and a major ninth. That gives the chord formula 1 - 3 - 5 - 6 - 9.
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