Use the Formula for the Sum of the First n Terms of a Geometric Sequence
-Find the sum of the first five terms of the geometric sequence: -2, -6, -18, . . . .
A) - 242
B) -26
C) 242
D) - 121

Question

Quizplus · Accepted Answer

The sum of the first n terms of a geometric sequence is given by $S_n = \frac{a(1 - r^n)}{1 - r}$, where $a$ is the first term, $r$ is the common ratio, and $n$ is the number of terms. Here, $a = -2$, $r = \frac{-6}{-2} = 3$, and $n = 5$. Plugging these values into the formula gives $S_5 = \frac{-2(1 - 3^5)}{1 - 3} = \frac{-2(1 - 243)}{1 - 3} = \frac{-2(-242)}{-2} = -242$.

Use the Formula for the Sum of the First N