The 3rd term of a geometric series is 18 , and the 5the term is 162 .Determine the sum of the of the first 7 terms ,where r < 0

Answer 1

162 = 18r^2
r = 3

18 = 9a, so a = 2

S7 = 2(1-3^7)/(1-3) = 2186

check:
2+6+18+54+162+486+1458 = 2186

Answer 2

Thanks for helping me

Answer 3

Yes

Answer 4

Everything is right, but
r = -3
not r = 3
because the problem stated that r < 0