f(x) = (2+x)/(1-x)

I got it to....

2 sigma x^n + sigma x^(n+1)

sigma goes from 0 to infinity

I'm looking at the solution and they get...

2 + Sigma 2(x^n) + Sigma x^n = 2 + (3)Sigma x^n

In this part Sigma goes from n=1 to infinity

Can someone explain how they got to this step?

P.S. I am so sorry about not putting into the correct type format.