How many terms of the G.P. 3, 32,34,.... be taken together to make 3069512 ?
3,32,34,....is a G.P.
and Sn=3069512,a=3,r=12
Sn=a(1−rn)1−r
3069512=3(1−(12)n)1−12
3069512=3×2×(2n−1)2n
1023.2n=1024.2n−1024
1024=2n
⇒210=2n
⇒n=10
How many terms of the G.P. 3,32,34..... are needed to give the sum 3069512 ?