There is 9 terms in the expansion so the middle term is the 5th.
(r + 1)th term of (a + b)^n = nCr a^(n-r) b^r
So here 5th term = (4 + 1)th term
= 8C4 (x^1/2)^(8-4) (y^1/2)^4
= 70 x^2 y^2 answer
