Question

How do you find `S_n` for the geometric series `a_1=5`, r=3, n=12?

Answer 1

`S_n = a_1 (r^n-1)/(r-1)`

hence plugging in the values,

`S_n = 5 ((3^12-1)/(3-1))`

`S_n = 5/2 (3^12-1)`