Learn Swedish: Forskaren tror att resultatet är rätt. - The researcher believes that the result is correct.

We use tror because the researcher is expressing a belief or an assumption about something factual (whether the result is correct or not). If they were expressing a personal opinion or taste, they would use tycker. Tänker is used for the active process of using your brain, like when you are actively pondering a problem.

Both forskaren (the researcher) and resultatet (the result) are definite words. Why do they have different endings?

It depends on the grammatical gender of the noun. Forskare is an en-word, so we add -n to make it definite, giving us forskaren. Resultat is an ett-word, so we add -et to make it definite, resulting in resultatet.

Since resultatet is an ett-word, shouldn't the adjective rätt get an extra -t at the end?

Usually, yes! Adjectives describing ett-words get a -t added to them. However, because rätt (correct) already ends in a double -tt, its spelling doesn't change. It looks exactly the same for both en-words and ett-words.

Can I leave out att in Swedish, just like we often drop the word that in English?