Why can't it be "den egyptisk kysten"? It just seems like usually the adjectives ending in "e" are for plural nouns
I was confused about the same thing and asked a question. I got an answer in this discussion from z0l6dier saying, "You use the plural (definite) form of the adjective in "the + adjective + noun" constructions."
Why can't you use 'coastline' interchangeably with 'coast' for kyst?
I think that would be closer to 'kystlinje'.