Learn Polish: Musisz sprawdzić wasze wyniki. - You have to check your results.

wasze is the plural form of "your" (referring to a group of owners). It is in the accusative case because it describes the direct object of the sentence, wyniki (results). For non-masculine-personal nouns, the accusative plural pronoun is wasze.

The verb musisz means "you (singular) must". Why are we using the plural "your" (wasze)?

This happens when you are talking to one person about something that belongs to them and at least one other person. For example, a manager telling a team leader, "You (singular) must check your (the team's) results." If the results belonged only to the person being spoken to, it would be twoje wyniki.

How do we know wyniki is in the accusative case if it looks like the nominative case?

You can tell from its job in the sentence! wyniki is the direct object receiving the action of the verb sprawdzić (to check), which requires the accusative case. For inanimate objects like wynik (result), the accusative plural shares the exact same form as the nominative plural.

Why is it sprawdzić and not sprawdzać?

sprawdzić is the perfective version of the verb "to check". It is used here because the focus is on finishing a single, specific action. You need to complete the check, not do it as a continuous or repeated habit.