Q 54. - Calculus

Question

Determine whether the series $\sum _{k=0}^{\infty }{\left(\frac{-9}{8}\right)}^k$ converges or diverges. Give the sum of the convergent series.

Step-by-Step Solution

Answer

The series $\sum _{k=0}^{\infty }{\left(\frac{-9}{8}\right)}^k$ diverges.

Step 1. Given information.

Given a series $\sum _{k=0}^{\infty }{\left(\frac{-9}{8}\right)}^k$.

Step 2. Find if the series converges or not.

The series $\sum _{k=0}^{\infty }{\left(\frac{-9}{8}\right)}^k$ is in the standard form $\sum _{k=0}^{\infty }c{r}^k$ for a geometric series with $c=1$ and $r=-\frac{9}{8}$.

The geometric series converges if and only if $\left|r\right|<1$.

Since $r=-\frac{9}{8}$, it follows that the series $\sum _{k=0}^{\infty }{\left(\frac{-9}{8}\right)}^k$ diverges.