Questions & Answers about Egzamin był trudny, ale mój wynik jest dobry.
Polish does not have articles like English the and a/an.
So:
- Egzamin can mean the exam or an exam
- wynik can mean the result or a result
You understand which one is meant from context. In this sentence, Egzamin is naturally understood as the exam, and mój wynik as my result.
Both are in the nominative case because they are the subjects of their clauses:
- Egzamin był trudny = The exam was difficult
- mój wynik jest dobry = my result is good
In Polish, the noun after być can stay in the nominative when you are describing what something is like with an adjective, as in:
- egzamin był trudny
- wynik jest dobry