Sum 1+r+r2+⋯+rn1+r+r^2+\dots+r^n1+r+r2+⋯+rn.
(rn+1−1)/(r−1) (r^{n+1}-1)/(r-1)(rn+1−1)/(r−1)
rn−1r^n-1rn−1
r(n+1)r(n+1)r(n+1)
None