The main result in (d), with the base approaching 1/e, was from Alt, Guibas, Mehlhorn, Karp, and Wigderson (1996) (Theorem 3), who also obtained other results in related settings.
(For specifically the min-area triangle problem, Prof. X is probably wrong, since the problem is "3SUM-hard" and is conjectured not to be solvable in n^{2-delta} time for any positive constant delta.)