Learn Turkish: Biz güçlü müyüz?

In Turkish, the yes/no question particle changes to match the last vowel of the word before it using 4-way vowel harmony. Since the last vowel in güçlü is ü, the question particle must take the form mü.

Why is there a y in the middle of müyüz?

The y acts as a buffer letter. The question particle is mü and the personal suffix for 'we' is üz. Because Turkish generally avoids putting two vowels right next to each other, the y is inserted to smoothly connect them, creating mü-y-üz.

Where is the word for 'are' in this sentence?

There is no standalone word for 'are' in Turkish. Instead, that meaning comes from the personal suffix attached to the very end of the sentence. The -üz in müyüz is the piece that translates to 'we are'.

Could I just say Güçlü müyüz? without Biz?

Yes, you can! Because the personal suffix -üz already makes it perfectly clear that the subject is 'we', dropping biz is very common and natural. Including biz just puts a little extra emphasis on the 'we'.