Chapter 8.3, Problem 71PE

For Exercises 49-72, find the sum of the geometric series, if possible. (See Examples 6-8)

${\displaystyle \underset{n=3}{\overset{\infty }{\sum }}4{\left(\frac{1}{2}\right)}^{n-1}}$ (Hint: Evaluate the infinite sum from $n=1$

to infinity. Then subtract the terms corresponding to $n=1$ and $n=2$.