In the expansion of (x+a)n, if the sum of odd terms be P and sum of even terms be Q. Consider the following statements:
(i) P2−Q2=(x2−a2)n
(ii) P2+Q2=(x2+a2)n
(iii) 4PQ = (x+a)2n−(x−a)2n
(iv) P - Q = (x−a)n
Then the correct statement are: