Find the sum of the first n terms of the following arithmetic sequence.
-$a 1 = 4 , d = - 2 ; \quad n = 5$
A) -20
B) 20
C) 0
D) -6

Question

Quizplus · Accepted Answer

The sum of the first n terms of an arithmetic sequence is given by the formula $S_n = \frac{n}{2} [2a_1 + (n-1)d]$, where $a_1$ is the first term, $d$ is the common difference, and $n$ is the number of terms. Plugging in the given values, we get $S_5 = \frac{5}{2} [2(4) + (5-1)(-2)] = \frac{5}{2} [8 + 4(-2)] = \frac{5}{2} [8 - 8] = \frac{5}{2} \cdot 0 = 0$.

Find the Sum of the First N Terms of the Following