Question

Proving summation without using induction

I don't understand the part after (r-1)(ar ... ) and so on, where did (r-1) go?

Answer 1

plz see the other answer w/ corrections below

Explanation:

4th row should instead be: r*Sk - Sk = ar^(k+1) - ar^0

(r-1)Sk = ar^(k+1) - a

Sk = (ar^(k+1) - a) / (r-1)

Answer 2

hope it can help you

k,i=0 ∑ a
`r^(i)` =
`S_(k)`