Asked by Edward

the 3th term of a GP is 63 while it 5th is 567.what is the sum of it's first seven terms
Answered by oobleck
r^2 = 567/63 = 9
r = ±3
ar^2 = 63, so a = 7
and as usual,
S7 = a(r^7-1)/(r-1)