Units 3/4 Cambridge 6K W.E 37

[Prerna94]

Hello can anyone please explain W.E 37? I understand odd and even graphs but I don’t understand this example.
It’s notation is so different to W.E 35.

[S_R_K]

If n is even, then (–1)^n = 1. If n is odd, then (–1)^n = –1.

Compare WE35c to WE37a. What they are doing in WE37a is using the (–1)^n notation to avoid having to write out the solutions in two parts, like they have done in WE35c.