In the summation of series of terms in GP when to use : S = a(r n -1)/(r-1) and S = a(1-r n )/(1-r)

Question

Ashwin Muralidharan IIT Madras · Answer

Hi Suhas, Both are one and the same. You can use either one of those. Except for the case when r=1 (when the series is not a GP). Regards, Ashwin (IIT MadraS).

Swapnil Saxena · Answer

Both are same, so it doesnt really matter . u can use any one of them in any type of question. however mostly we use a(1-rⁿ)/(1-r) when r is fractional and less than 1 ,and a(rⁿ-1)/(r-1) when r is integral or more than 1.

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In the summation of series of terms in GP when to use : S = a(r n -1)/(r-1) and S = a(1-r n )/(1-r)

In the summation of series of terms in GP when to use : S = a(rⁿ-1)/(r-1) and S = a(1-rⁿ)/(1-r)

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In the summation of series of terms in GP when to use : S = a(r n -1)/(r-1) and S = a(1-r n )/(1-r)

In the summation of series of terms in GP when to use : S = a(rn-1)/(r-1) and S = a(1-rn)/(1-r)

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In the summation of series of terms in GP when to use : S = a(rⁿ-1)/(r-1) and S = a(1-rⁿ)/(1-r)