Augmented and Diminished Intervals
A Double Augmented 2nd is the same as a Major 3rd.
A Diminished 3rd is the same as a Major 2nd.
A Diminished 4th is the same as a Major 3rd.
An augmented 2nd is the same as a Minor 3rd.
Forum Music Theory
A Discussion on Music Theory
Triads
How do you know which triads are major and which are minor in a given key?