The sum to $n$ terms of a GP with first term $a = 2$ and ratio $r = 3$…

Question

The sum to $n$ terms of a GP with first term $a = 2$ and ratio $r = 3$ is:

Accepted Answer

C. $S_n = 2(3^n - 1)/(3 - 1) = 3^n - 1$, by the GP formula

$S_n = a(r^n - 1)/(r - 1) = 2(3^n - 1)/2 = 3^n - 1$.

Answer

$2(3^n + 1)/2$, missing the $-1$ in the formula here

Answer

$2\cdot 3^n$, ignoring the sum formula entirely

Answer

$2n\cdot 3^{n-1}$, the term-by-term sum on the worksheet