Mathematics - Sequence & Series Question with Solution | TestHub

$a_1{r}^5=4a_1{r}^3$, so $r^2=4$ and $r=2$ (increasing). $\begin{array}{rlr}& a_1{r}^8-a_1{r}^6=192,\text{ so }256a_1-64a_1=192\text{ and }{a}_1=1.& \sum \frac{1}{a_i}=1+\frac{1}{2}+\frac{1}{4}+\cdots =\frac{1}{1-\frac{1}{2}}=2.\end{array}$