`A -: B = A/B` `= (81^x - 1)/(9^x - 1)` `= ((9^x)^2 - (1)^2)/((9^x - 1))` `= ((9^x - 1)(9^x + 1))/(9^x - 1)` `= 9^x + 1` [ ন. প্র. য. বো ]