Answer:
24x²y²
Step-by-step explanation:
For k=0 to n, the k-th term of (a+b)^n is ...
(nCk)·a^(n-k)·b^k
You want the k=2 term for the n=4 expansion with a=2x and b=-y.
Then the third term of the expansion is ...
(4C2)·(2x)^2·(-y)^2 = 6·4x^2·y^2 = 24x^2y^2
_____
nCk = n!/(k!(n-k)!)
4C2 = 4!/(2!·2!) = (4·3)/(2·1) = 6
