Still on 145. Moved onto II - translate into Latin
Number 3. The answer gives the plural acc of inimicus (inimicos) with a short o. Is this just because there’s no need as it will always be long? Or have I yet again missed the point? If so, don’t tell me how, I’ll go back and investigate.
Thanks.
It’s a mistake. Well spotted. Did you get the other long vowel?
By the way most texts other than those specially prepared for students don’t have macron markings.
Yes, I realise that. Pretty essential for us beginners though, no?
A lot of people when writing in Spanish leave off the accents. After all, everybody knows that the first a in águila is stressed, so why bother with the diacritics? I disagree intensely. Not only because I’m a pedant, but even with context, there is often ambiguity. It seems to me that in Latin, without macrons, certainly amongst non-experts, there will be a lot of head-scratching.
In the first place information on the length of vowels can be found in the dictionary. You can see some general rules in Allen and Greenough and other grammars eg here https://dcc.dickinson.edu/grammar/latin/general-rules-quantity
Of course, the ancient Romans themselves never used macrons. As for how essential they are, that depends. If you use the traditional accent, yeah. If you use the Spanish one (like me), or the Italian (Ecclesiastical or Church Latin), not so much. I do agree that it’s trivial, though. 
The grandfather of the macron: Apex (diacritic)
Fascinating. I was not aware of this usage.
The Hermeneumata Pseudositheana, a post-classical (3rd century A.D.) set of phrasebooks to teach Latin to Greek speakers, does not use macrons. At least, the transcription on the Bibliotheca Augustana doesn’t.
(http://www.hs-augsburg.de/~harsch/Chronologia/Lspost03/Dositheus/dos_col0.html) I don’t know if the MSS used for the edition (Goetz, Leipzig, 1892) used them or not.
An interesting question, for sure.
Of course, the ancient Romans themselves never used macrons. As for how essential they are, that depends.
Ancient texts do lots of things, like not using word division, which I dont think anyone nowadays would advocate!
Knowing the lengths of vowels is of course crucial if you are reading verse.
It isn’t a trivial question at all and I was glad that the OP raised it.