## Calculus (3rd Edition)

$\sum_{n=0}^{\infty} \frac{(-1)^n}{2^n}$ converges absolutely.
We have $$\sum_{n=0}^{\infty} |\frac{(-1)^n}{2^n}|=\sum_{n=0}^{\infty} (\frac{1}{2})^n$$ which is a geometric series with $|r|=|1/2|\lt 1$, which converges. Then $\sum_{n=0}^{\infty} \frac{(-1)^n}{2^n}$ converges absolutely.