
Summing a series problem
Hi There, i am trying to sum up a sequence of numbers using the
summing rule for
1 + a^1 + a^2 + a^3 + a^4 +... + a^n = (a^n  1/(a1),
for this sequence:
1/9 + 1/9^2 + 1/9^3 + .. + 1/9^n.
Is it as simple as just inverting the formula ie :
((a^n  1/(a1))^1 ?? What about the 1 that doesn't exist at the
beginning, normally i would subract a 1 after my calculation but if I
do that here the answer will be negative.
Any help appreciated
Many thanks

the sum is $\displaystyle \frac{a^{n+1}1}{a1}$ and put $\displaystyle a=\frac19.$