Semitic languages tend to have two forms for second person pronouns, masc and fem: classical Hebrew אתה (masc), את (fem)--although את is also masc in rabbinic Hebrew--Syriac ܐܢ̄ܬ (masc, pronounced at, the nun is not pronounced), ܐܢ̄ܬܝ (fem, pronounced at, the nun and yod at end are silent). Anyway, the fatha line above the ta letter means masc while the kasra line below is fem, as JasonVoorhees noted. ݀You can see the nun in the Syriac and in (Imperial and Middle) Aramaic אנת (e.g., Ezra 7:25; Dan 6:17; which becomes את common 2nd sg in Qumran and Late Aramaic dialects--note the Syriac above both are pronounced "at," so also Jewish Palestinian Aramaic and Christian Palestinian Aramaic). You can see the nun in both the ketib, אנתה, at Dan 2:29, and the Qere אנת. I mention all this because the nun in Arabic is found in other Semitic languages although not always pronounced, and you can also see a parallel to kasra in the Syriac yodh even though the yodh is not pronounced.
I bought A.S. Tritton's "Teach Yourself Arabic", which you suggested in a few threads. I was expecting a full size 8" X 11" textbook, but it is a pocket book size paperback, about 7" X 4.75". It was published by Kitab Bhavan out of New Delhi. The Arabic print is even smaller than Duolingo's. The reprint date of this book is 2017. Is this the same edition you have?
Sorry if I mislead you. The publication page of my copy says the impression is from 1977. But it's likely the identical book, as mine is the same size. Frankly, I got it as a hand-me-down so use it to get some background info that DL doesn't provide. But, yes, the print size is not ideal. I got a couple of other books that are bigger: Fischer, A Grammar of Classical Arabic (Third revised edition, 2002) but that still has small print for my eyes, and Jones, Arabic Through the Quran (Islamic Texts Society, 2005), which has the most legible print. I personally think it's good to have several such grammars as aids and then find the one that works best for you. If you find one, please let us know. I personally find Tritton, like DL, helpful despite the drawbacks. [Addendum: A magnifying glass would help!]
No, you didn't mislead me. I just thought the book, and the text, would be bigger. Also, the title page says the "First Indian Edition" was 1943 so I was wondering if there was an earlier British edition. The English syntax/style sounds much older than 1943 to my ears. Do you use a magnifying glass to read the Arabic by any chance? The print is so tiny, no human being could write that small.