Question Number 56413 by gunawan last updated on 16/Mar/19
$$\mathrm{The}\:\mathrm{solution}\:\mathrm{of}\:\mathrm{the}\:\mathrm{equation} \\ $$$$\mathrm{1}+{a}+{a}^{\mathrm{2}} +{a}^{\mathrm{3}} +...+{a}^{{x}} =\left(\mathrm{1}+{a}\right)\left(\mathrm{1}+{a}^{\mathrm{2}} \right)\left(\mathrm{1}+{a}^{\mathrm{4}} \right) \\ $$$$\mathrm{is}\:\mathrm{given}\:\mathrm{by}\:{x}\:=\:\_\_\_\_\_. \\ $$
Commented by mr W last updated on 16/Mar/19
$${last}\:{term}\:{of}\:{LHS}\:{is}\:{a}^{{x}} \\ $$$${last}\:{term}\:{of}\:{RHS}\:{is}\:{a}^{\mathrm{7}} \\ $$$$\Rightarrow{x}=\mathrm{7} \\ $$