What is the formula for a a regular 7 diminished triad, and a half diminished triad?
~Long live the 6-string~
Fully diminished and half-diminished chords are not triads. They are 4 note chords.

Dimnished Triad-1 b3 b5
Fully Diminished Chord-1 b3 b5 bb7 (the bb7 is a double-flat 7, enharmonic to 6)
Half Diminished-1 b3 b5 b7

With C as the root, the chords are:
Triad-C Eb Gb
Full-C Eb Gb Bbb
Half-C Eb Gb Bb

Edit: Bbbb, WTF?
Last edited by bangoodcharlote at Jul 21, 2006,
Well first off saying " a diminised 7 triad" is kinda funny, because a triad is 3 notes, and a 7th chord is 4 notes.
A triad will be some form of root, third, and fifth...in the case of diminished triad that will be :
1, b3, b5
And the fully diminshed 7th:
1, b3, b5, bb7
Finally the half diminised 7th( otherwise known as minor7(b5):
1, b3, b5, b7

Thats the short answer to your question. I would recommend really mastering triads first before moving on to 7th chords, as they all contain at least one triad.
bang, you are correct saying A, as the enharmonic spelling, but it would be a "B double flat" ( Bbb), not B triple flat. And calling it Bbb is most technically correct, because of its function in a Cdim7 setting.