A triad is typically made up of three notes, which include the root, the third, and the fifth of a scale. Based on the notes you've mentioned (A and C), we can analyze several triads.
- A minor triad: The notes are A (root), C (minor third), and E (perfect fifth).
- C Major triad: The notes are C (root), E (major third), and G (perfect fifth).
- C minor triad: The notes are C (root), E♭ (minor third), and G (perfect fifth).
Since you have the notes A and C:
- If you're considering A minor (A, C, E), the additional note would be E.
- If you're considering C and looking at triads, you would normally add E or G, depending on whether it’s a major or minor triad.
Therefore, the notes you could consider adding to A and C for various triads include E (for A minor) and possibly E or G (for the C major/minor context).
If you have a specific context or type of triad in mind, that could further refine the possibilities!