u know the sum of 1^2-2^2+3^2-4^2+...(2n-1)^2-(2n)^2=-n(2n+1)
u have extra term=(2n+1)^2
so just add these two to get ur final sum as:
-n(2n+1)+(2n+1)^2
so (2n+1)(-n+2n+1)
sum=(2n+1)(n+1)
of a part
because u have already found out from the previous question
the sum 1^2-2^2+3^2-4^2+...(2n-1)^2-(2n)^2=-n(2n+1)
in these type of questions u use what u have proved above