In a G.P, the product of the second term and fourth term is double the fifth term and the sum of the first four terms is 80. Find the G.P.

Answer 1

(ar)(ar^3) = 2ar^4
a^2r^4 = 2ar^4
ar^4 = 2r^4
a = 2

a(r^4-1)/(r-1) = 80
1+r+r^2+r^3 = 40
r = 3

So, the GP is 2,6,18,54,162,...
(6)(54) = 2*162
2+6+18+54 = 80

Answer 2

i didn't know it

Answer 3

How did you get 3