Find the sum of the GP :


Find the sum of the GP :

1 + 3 + 9 + 27 + …. To 7 terms



Sum of a G.P. series is represented by the formula $\mathrm{S}_{\mathrm{n}}=\mathrm{a} \frac{\mathrm{r}^{\mathrm{n}}-1}{\mathrm{r}-1}$

when r>1. ‘Sn’ represents the sum of the G.P. series upto nth terms, ‘a’ represents the first term, ‘r’ represents the common ratio and ‘n’ represents the number of terms.


a = 1

r = (ratio between the n term and n-1 term) 3 ÷ 1 = 3

n = 7 terms

$\therefore \mathrm{S}_{\mathrm{n}}=1 \frac{3^{7}-1}{3-1}$

$\Rightarrow \mathrm{S}_{\mathrm{n}}=\frac{2187-1}{3-1}$

$\Rightarrow \mathrm{S}_{\mathrm{n}}=\frac{2186}{2}$

$\Rightarrow \mathrm{S}_{\mathrm{n}}=1093$


Leave a comment


Click here to get exam-ready with eSaral

For making your preparation journey smoother of JEE, NEET and Class 8 to 10, grab our app now.

Download Now