Question

Find the sum of the GP : 

1 + 3 + 9 + 27 + …. To 7 terms

Answer 1

Sum of a G.P. series is represented by the formula,\(S_n = a\frac{r^n - 1}{r-1}\) , when r>1. 

‘Sn’ represents the sum of the G.P. series up-to n^th terms, ‘a’ represents the first term, ‘r’ represents the common ratio and ‘n’ represents the number of terms.

Here, 

a = 1 

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

n = 7 terms