The problem (2a) is stated:
[![enter image description here](https://i.stack.imgur.com/a2d0I.png)](https://i.stack.imgur.com/a2d0I.png)
[![enter image description here](https://i.stack.imgur.com/7wd8L.png)](https://i.stack.imgur.com/7wd8L.png)

Why is $P(X>x) = 2^{-x}$ and not the sum $\sum\_{i=x}^{\infty} 2^{-x} = 2^{-x+1}?$ I'd like to make sure I'm not misunderstanding something fundamentally.