Find the requested sum for the arithmetic sequence.
-$a_{n}=-3 n-9 ; S_{5}$
A) -60
B) 0
C) -90
D) -24

Name: Find the requested sum for the arithmetic sequence. -$a_{n}=-3 n-9 ; S_{5}$ A) -60 B) 0 C) -90 D) -24
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Question

Quizplus · Accepted Answer

The sum of the first n terms of an arithmetic sequence is given by $ S_n = \frac{n}{2} (a_1 + a_n) $. Here, $ a_1 = -3(1) - 9 = -12 $ and $ a_5 = -3(5) - 9 = -24 $. Thus, $ S_5 = \frac{5}{2} (-12 - 24) = \frac{5}{2} \times (-36) = -90 $.

Find the Requested Sum for the Arithmetic Sequence an=−3n−9;S5a_{n}=-3 n-9 ; S_{5}an​=−3n−9;S5​

Find the Requested Sum for the Arithmetic Sequence $a_{n}=-3 n-9 ; S_{5}$