Answer:
1
Step-by-step explanation:
Sum of nth term of a GP is expressed as;
Sn = a(r^n-1)/r-1
The sum of the first 8 terms of a GP is expressed as;
S8 = a(r^8 - 1)/r-1
The sum of first 4 terms is expressed as;
S4 = a(r^4 - 1)/r-1
If the sum of the first 8 terms of a GP is five times the sum of first 4 terms then
S8 = 5S4
a(r^8 - 1)/r-1 = 5[a(r^4 - 1)/r-1]
r^8 - 1 = 5(r^4 - 1)
r^8 - 1 = 5r^4 - 5
r^8 - 5r^4 = -5+1
r^4(r^4 - 5) = -4
r^4 - 5 = -4
r^4 = -4+5
r^4 = 1
r = 1
Hence the common ratio is 1
