How to solve Energy and Power in digital signals

gatlin762

1. The problem statement, all variables and given/known data
Determine if the discrete-time exponential signal is an energy signal or power signal
x(n) = 2(0.5)ⁿ

2. Relevant equations
My professor said to start off by verifying if it is a geometric sequence with this formula (which I don't understand)
Ʃqⁿ from n=N₁ to N₂


3. The attempt at a solution
No idea how the geometric sequence formula works.