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I understand that its multiplied by 'r'. But why do we stop the series and n-1?
please read the following extract
" Algebraically, we can represent the n terms of the geometric series, with the first term a, as:
Sn=a+ar+ar^2+ar^3+...ar^n-1 [1]
Each term is the previous term times r, so we can try multiplying the series by r
rSn=ar+ar^2+ar^3+...+ar^n-1+ar^n [2]
Subtracting Equation 2 from Equation 1, we get:
(1-r)Sn=a-arn "
Here in [1]- i dont understand why we stop at ar^n-1 when we have to find the sum of terms upto 'n' &
in [2]-what is the effect of adding r to the series and also why here have we extended the term upto ar^n but not in [1]
Kindly elaborate.
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