Find the sum of the first 10 terms of the geometric sequence 12000 1200 120 12 1.2

1, - 4, - 9, - 14, this is arithmetic sequencewith difference = d = - 5 a12 = a1 + (n-1) d = 1 + (12-1) (-5) = 1 + (11) (-5) = 1 - 55 = - 54 sum of the first 12 terms = (n/2) * (a1 + a12) = 12/2 (1-54) = 6 (-53) = - 318