Find S7 for the geometric series 2 + - 6 + 18 + - 54 + ...

1094

Step-by-step explanation:

The sum of terms of a geometric series is given by ...

Sn = a1· (r^n - 1) / (r - 1)

You want the sum for ...

a1 = 2, r = - 3, n = 7

Filling in the numbers, we get ...

S7 = 2· ((-3) ^7 - 1) / (-3-1) = 2 (-2188) / (-4)

S7 = 1094