Sum the series
Sn = a + (a+d)r + (a+2d)r^2 + ... + [a+(n-1)d]r^(n-1)
n-1
Sum (a+nd)r^n
n=0
Presumably I need to split this up into a sum of ar^n and ndr^n
I have already summed ar^n, how would I go about summing ndr^n ?
Hey thanks for the solution, I've already handed in the work alas without the proof of that question, but at least now I know the logic behind working out a complicated summation like that (complicated on my level, anyway)
I've also read the other solution which requires calculus, thanks alot