Respuesta :

CRAZYBU113T
The above series is a Geometric series because:
t2/t1 = t3/t2  --> 14/7 = 28/14 --> 2 = 2
and common ratio (r)=2
The for S12 we have,
    S12 = a(1 - r^12) /(1-r) where, a = first term = 7
 or, s12 = 7*(1 - 2^12) / (1 - 2)
             = 28665