Answer: Learning dominant 9th (or simply 9th) guitar chords is a logical continuation to dominant seventh chord study. Theoretically ninth chords are built with 5 notes called root (1), major third (3), perfect fifth (5), minor seventh (b7) and ninth (9).
We will see that it is quite unusual to play these five notes together on the guitar. As it is shown in the chart below, a dominant 9th chord is simply a dominant seventh chord with a ninth added.
