"Dette kommer dere til å angre."
Translation:This you are going to regret.
The previous sentence shows å angre followed by på... How to know when I should use it... Questions only?
Sentence - Hva angrer du på i livet?
You can include 'på' here, and the sentence will still be natural.
I have been puzzled over this form of sentence for a while now, because of the "det" or "dette" at the beginning. I know what it means but I am not sure when to use it. Would you ever say "Dere kommer til å angre dette"?
I'm not a native but I think that you could say that. If you want to emphasize "dette" you put it in the beginning and change the word order so that the verb is at the second place of the sentence.
The English translation would not often be appropriate. In nearly all circumstances only the translation, "You are going to regret this," would be appropriate.