### Home > PC3 > Chapter 12 > Lesson 12.1.3 > Problem12-42

12-42.

In the method shown in the Math Notes box, the series ended with $ar^{(n−1)}$. Why is the power $\left(n − 1\right)$ and not $n$, if there are $n$ terms in the sequence?

Instead of going from $1$ to $n$, the series goes from __ to $n − 1$.