Question Number 5783 by Rasheed Soomro last updated on 27/May/16
$$ \\ $$$$\mathcal{D}{etermine}: \\ $$$${a}^{{a}} +\left({ar}\right)^{{a}+{r}} +\left({ar}^{\mathrm{2}} \right)^{{a}+\mathrm{2}{r}} +…+\left({ar}^{{n}ā\mathrm{1}} \right)^{{a}+\left({n}ā\mathrm{1}\right){r}} \\ $$