I was given a sum s, then I expressed it using sigma notation as you can see below. Now, I am supposed to find the closed form values for the said sum as shown in eq.2, but I am stuck at eq.1. I don't know how to deal with the highlighted part, am I forgetting something or did I make some mistake? Grateful for any help!
$$(-1)^{2n}=((-1)^2)^n=1^n=1$$