Find the partial sum.
-Find the sum of the first five terms of the sequence whose general terms is $\mathrm { a } _ { \mathrm { n } } = - 9 \mathrm { n }$.
A) $- 27$
B) $- 135$
C) $- 90$
D) 135

Question

Quizplus · Accepted Answer

The sequence is arithmetic with the first term $a_1 = -9$ and the common difference $d = -9$. The sum of the first five terms is given by the formula $S_n = \frac{n}{2} (2a_1 + (n-1)d)$. Substituting $n = 5$, $a_1 = -9$, and $d = -9$, we get $S_5 = \frac{5}{2} (2(-9) + 4(-9)) = -135$.

Find the Partial Sum an=−9n\mathrm { a } _ { \mathrm { n } } = - 9 \mathrm { n }an​=−9n

Find the Partial Sum $\mathrm { a } _ { \mathrm { n } } = - 9 \mathrm { n }$