Breakdown of Vi har extra biljetter, så du måste åka med oss.
du
you (singular)
vi
we
ha
to have
åka
to go, to travel, to leave
Questions & Answers about Vi har extra biljetter, så du måste åka med oss.
Why doesn't extra get a plural ending to match biljetter?
Extra is an indeclinable adjective. This means its spelling never changes, no matter if the noun it describes is an en-word, an ett-word, or plural. You will never add an -a or -t to the end of it.
Why use åka med here instead of just saying gå med?
Åka specifically means to travel using a vehicle, such as a train, car, or bus. Since they have biljetter (tickets), they are clearly using transportation. If they were walking, you would use gå. Another very common phrase for 'come with us' is följa med.
Why isn't there an att before åka?
Måste is a modal verb. Modal verbs are always followed directly by the infinitive form of the next verb, without using att (to). It works just like English, where we say 'must go' instead of 'must to go'.
After the comma and så, why is the word order du måste rather than the reversed måste du?
The word så (so) acts as a coordinating conjunction here, which means it joins two complete main clauses. Because the second clause is a standard main clause that begins with its subject (du), the verb (måste) simply takes its normal second place.