Need a little help with this one, Not sure how to proceed.
Two positive integers, are connected by the relation . By using a binomial expansion show that for all positive integral values of n the expression is exactly divisible by . By choosing suitable values of a and n, show that is divisible by 9, and hence that is divisible by 9.
I tried putting the substitution for into the equation, and did a binomial expansion of , but not sure where that is supposed to lead. It seems like another longer equation.
Thanks for your help.