Question

Find the sum of first six terms $\left(S_6\right)$ of the following G.P.
$1,3,9,....$

Answer 1

The given G.P. is $1,3,9,....$
Here, $a=1,r=\frac{3}{1}=3$
Now, $S_n=\frac{a(r^n-1)}{r-1}$ since $r>1$
$S_6=\frac{1(3^6-1)}{3-1}=\frac{1(729-1)}{2}=364$