A geometric sequence has all its terms positive. The first term is 7 and the third term is 28.

THIS IS FOR MATHS STUDIES, NOT MATHS SLThe question is from the 2014 specimen paper
First, find the common ratio:U1 = 7U3 = 28
(Identify Formula): Un = U1 x r^n-1 U3 = 7xr^3-1 28 = 7xr^2 r = 2
Then, find the sum of the first 14 terms:S14 = (7(2^14-1) / 14-1) = 114,681