Question about past tense conjugation [Nynorsk]
Hei! I've been learning norwegian nynorsk for around a month and overall making pretty decent progress. Learned some vocabulary, noun inflections, present and future tenses for verbs as well as the imperative forms, got some basics of working with adjectives and adverbs too. I can form my own sentences occasionally. My main resources are wikipedia, ordbøkene.no, the few online translators that do include nynorsk, and my wonderful norwegian girlfriend I can ask for some help from time to time.
I decided to take the plunge into learning the past tense and it was a little confusing but I think I mostly got it? Short verbs get -dde (å bu, bur, budde), verbs that in the present tense end with -ar now just end with -a (å kasta, kastar, kasta), and those that end with -er now end with either -te or -de (å kjøper, kjøper, kjøpte).
That last point is what I would like to ask about. Is there any way to know if it's gonna be te or de just looking at the infinitive? At first I thought it might be having a 'j' before the final vowel of the infinitive, because of the first example I saw being å byggje -> byggde, however that got pretty quickly debunked by å grypje -> grypte and a couple other examples.
Is there any trick to it, or some rule of thumb? Or is it one of those things you gotta learn for each word where is applies?