### Home > APCALC > Chapter 10 > Lesson 10.2.2 > Problem10-121

10-121.

Let $S = \displaystyle \sum _ { n = 1 } ^ { \infty } \frac { a ^ { n } } { n + 1 }$, where $a$ is a constant. Homework Help ✎

1. Does $S$ converge if $a = 1$? Justify your answer.

This is a variation of the harmonic series.

2. Does $S$ converge if $a = -1$? Justify your answer.

This is an alternating series.

3. For what values of $a$ does $S$ converge? Justify your answer.

$\text{Using the Ratio Test: }\lim_{n\to\infty}\Big|\frac{a^{n+1}/(n+2)}{a^n/(n+1)}\Big|<1$