If the AP has an odd number of terms, the middle term is the term at position ((n+1)/2)
If the AP has an even number of terms, there are two middle terms at positions (n/2) and (n/2 + 1)
Use the formula (T_k = a + (k-1)d) to find the required middle term(s)
For an odd number of terms, the middle term is (a + left(frac{n-1}{2}right)d)
For an even number of terms, the two middle terms are (a + left(frac{n}{2}-1right)d) and (a + left(frac{n}{2}right)d)