Question

For a G.P.
D) If t=20t= 160, find S7​

Answer 1

Answer:

S7=635

SOLUTION:-

$a{r}^{2} = 20 \\ a{r}^{5} = 160$

on solving both

a=5

r=2

$s7 = 5( {2}^{7} - 1) \div (2 - 1)$