Question

Find the 20th term Geometric progression 1, 4, 16, 64.......& how many number of term given sum of geometric progression is 5461

Answer 1

Hello

Here is your answer...

first we will calculate common ratio (R)
R= 4/1 = 4

then 20th term

a20 = ar^19
= 1×4^19
= 274877906944

now sum of terms is 5461

Sn = a(r^n - 1)/r-1
5461 = 1(4^n - 1)/3
5461×3 = 4^n - 1
16383+1 = 4^n
16384 = 4^n
4^7 = 4^n

hence No. of terms will be 7

hope it helps
#jerri