The general term of a sequence is given. Find the indicated partial sum.
-$$a _ { n } = ( - 1 ) ^ { n } ( 2 n ) ; s _ { 4 }$$
A)20
B)16
C)-20
D)4

Question

Quizplus · Accepted Answer

The partial sum $s_4$ of the sequence $a_n = (-1)^n(2n)$ for $n = 1, 2, 3, 4$ is calculated as follows: $$s_4 = a_1 + a_2 + a_3 + a_4 = (-1)^1(2\cdot1) + (-1)^2(2\cdot2) + (-1)^3(2\cdot3) + (-1)^4(2\cdot4) = -2 + 4 - 6 + 8 = 4.$$

The General Term of a Sequence Is Given an=(−1)n(2n);s4a _ { n } = ( - 1 ) ^ { n } ( 2 n ) ; s _ { 4 }an​=(−1)n(2n);s4​

The General Term of a Sequence Is Given $a _ { n } = ( - 1 ) ^ { n } ( 2 n ) ; s _ { 4 }$