Triad Shapes

1. Find the root. Measure the three gaps in semitones going upwards, wrapping round from the top note back to the bottom one. The root is the note just above the biggest gap. If all three gaps are equal, it is augmented and has no root to find. That is why inversion is not asked for those.
2. Name the quality from the two gaps above the root:
   4 then 3 → major  ·  3 then 4 → minor  ·  3 then 3 → diminished  ·  4 then 4 → augmented
3. Name the inversion from the lowest note: the root means root position, the 3rd means 1st inversion, the 5th means 2nd inversion.

Counting on the neck. One fret is one semitone. In this tuning the gaps between neighbouring strings, lowest pair first, are 5, 5, 5, 4, 5 semitones. G to B is 4 rather than 5, which is why sets 1-2-3 and 2-3-4 need a different shape from the rest.

Worked example (standard tuning). On strings 2-3-4: D string fret 2, G string open, B string fret 1. Those are E, G and C. The gaps going up are E→G 3, G→C 5, then C wrapping round to E 4. The biggest is 5, so the root is the note above it: C. Above C the gaps run 4 then 3, so it is major. The lowest note is E, which is the 3rd, so 1st inversion. That makes it C major, 1st inversion.