When in English you would write "the [adjective] [noun]", the adjective always takes the e-form in Danish. For example:
The beautiful house = Det smukke hus, but; The house is beautiful = Huset er smukt
The kind cat = Den venlige kat, but; The cat is kind = Katten er venlig
The big people = De store mennesker, and; The people are big = Menneskerne er store
Xneb, I'm pretty sure you've replied this same answer to someone else regarding another word, but thanks for repeating it because I keep forgetting this somehow and your comments remind me! I've just given you a lingot for that.
(Come to think of it, I have learnt so much from reading the comments on Duolingo. This is why I prefer to do Duolingo on my laptop everyday rather than using my Android app.)
Apologies if it wasn't clear. The "the" inside the quotation marks is important. It has to be "the [adjective] [noun]" (or in Danish, "den/det/de [adjective] [noun]".)
Your examples use the indefinite articles, so the adjectives' forms depend on the gender (or if it's plural) of the noun they are describing. So it is, for example:
"Et smukt hus" (from trennerdios' example I missed a year ago.)
But it would be:
"Det smukke hus".
Hopefully this clears it up.
It can make sense if you're referring to two different types of the same item for example.
If you're looking at a big car compared to a small car, you could say you like the opposite model - meaning you like the small model rather than the big model as they are polar opposites. Sorry its a pretty bad example, but its all I've got at 8am - all I know is it makes sense in english