Use the partial sum formula to find the partial sum of the given arithmetic sequence.
-Find the sum of the first eight terms of the arithmetic sequence: 10, 15, 20, . . . .
A) 220
B) 45
C) 120
D) 440

Question

Quizplus · Accepted Answer

The partial sum formula for an arithmetic sequence is $S_n = \frac{n}{2}(a_1 + a_n)$, where $S_n$ is the sum of the first $n$ terms, $a_1$ is the first term, and $a_n$ is the nth term. Here, $n = 8$, $a_1 = 10$, and $a_n = a_1 + (n-1)d = 10 + (8-1)5 = 45$. Thus, $S_8 = \frac{8}{2}(10 + 45) = 4 \times 55 = 220$.

Use the Partial Sum Formula to Find the Partial Sum