Learn Turkish: Matematik zor mu? - Is mathematics difficult?

In Turkish, there is no separate word for 'is' or 'are' in simple sentences like this. It is just understood from the context! Literally, this sentence reads as 'Mathematics difficult [question]?'.

Why is the question word mu here instead of mı or mi?

The question particle changes its vowel to match the last vowel of the word right before it, following the rules of 4-way vowel harmony. Because the word zor has the vowel 'o', the question particle must take the 'u' sound, becoming mu.

Why does mu go at the very end of the sentence?

The question particle comes immediately after the specific word you are asking about. Here, you are asking if math is difficult, so mu comes right after zor. If you moved it and said Matematik mi zor?, you would be asking 'Is it mathematics that is difficult (or is it some other subject)?'.