if you look at your three notes and say for example that they are G E C.
Then you know that the chord will either be G E or C major.
The triad consists of the 1st 3rd and 5th notes on the scale or in other words the first three notes of the arpeggio.
So say you were gonna see if its C E or G major and you checked G first you can go G A B C D E F# G and see that the first third and fifth notes are G B D which is different to G E C. Then say you try C and write out the scale, you will find that C E G is the triad (first third and fifth) which is the same as G E C (order doesn't matter).
Good luck on wednesday
This is what I do
First of all, look at the key of the piece. Let's just do a random one and say D Major for an example. Then write out your chords - you never write out chord III, it's not on the JC course.
I - D F(sharp) A
II - Em G B
IV - G B D
V - A C(sharp) E
VI - Bm D F(sharp)
To clarify, chords II and VI are always minor! If you do not say Minor, that's incorrect then what you write down. Also make sure you write in your sharps and flats.
Then look at the notes at X / Y or whatever it calls it on the paper, name them and then look at your chords. See which chord fits the three notes. By the way, the first note of each chord tells the name of the chord. See the D Major chords for example:
I - D F(sharp) A - D Major chord
II - Em G B - E Minor chord
IV - G B D - G Major chord
V - A C(sharp) E - A Major chord
VI - Bm D F(sharp) - B Minor chord
I hope this makes things easier for you. (Mathswhiz101 you're kind of confusing me tbh of the way you described it here) But yeah when doing these, make sure it's the 1st, 3rd and 5th notes.