Learn Polish: Zamówiliśmy potrójną kopię dokumentu. - We ordered a triple copy of the document.

Potrójną is the multiplicative adjective potrójny (triple). It is formed by combining the prefix po-, the number root -trój-, and the adjective suffix -ny. It takes the -ą ending because it is in the accusative case to match the feminine noun kopię (copy), which is the direct object of the verb.

If we wanted to use the adverb form taught in this lesson, could we say Zamówiliśmy kopię trzykrotnie?

Yes, but it changes the meaning. Zamówiliśmy potrójną kopię means you ordered one item that is a triple copy (like a multipart document). If you say Zamówiliśmy kopię trzykrotnie, you are using the adverb trzykrotnie (three times) to modify the verb, meaning you performed the action of ordering a standard copy on three separate occasions.

Why does the word dokument take the -u ending here instead of -a?

Dokumentu is in the genitive case because it translates to 'of the document' (modifying kopię). The genitive singular endings for masculine inanimate nouns can be tricky, but loanwords, abstract concepts, and substances usually take the -u ending. Since dokument is a borrowed word, it takes -u.

What is the imperfective equivalent of zamówiliśmy?