In the expansion of `(x+a)^n` if the sum of odd terms is `P` and the sum of even terms is `Q ,` tehn `P^2-Q^2=(x^2-a^2)^n` `4P Q=(x+a)^(2n)-(x-a)^(2n)` `2(P^2+Q^2)=(x+a)^(2n)+(x-a)^(2n)` none of these