Only #1 seems too awkward as far as the beginning is concerned. The main problem is the ending, which I would change to: (2) The rate of frequency change must be negligible. (3) The frequency change rate must be negligible.
New words, one handy idiom, and a 2-minute quiz — delivered to your inbox to keep your streak alive.
Mister Micawber The main problem is the ending,Unexpected outcome! :-) I remember seeing a few dozen examples with "negligibly small" in GLOWBE...
MUSCOVITEIs it somehow possible to explain why "negligibly small" sounds bad to native speakers?Not to other native speakers necessarily, but to me. 'Negligible' means very unimportant or small.
Mister MicawberNot to other native speakers necessarily, but to me. 'Negligible' means very unimportant or small.Aha... I see.
MUSCOVITEYou will agree that the combination "infinitesimally small" is widely used in math, etc. books?No; I'd have to see such statistics.
MUSCOVITEDoes "infinitesimally small" sound ok to you?On a casual level, yes (just as with negligibly so), but when being careful, not at all.
fivejedjonbut I find them tautologous."being tautologous" - that is the clue to the puzzle! :-)