# Chapter 10 - Review Exercises - Page 1124: 9

$-20$

#### Work Step by Step

In order to calculate the first $4$ terms of the sequence we will have to plug $n=1,2,3,4$ into the given equation. So, we get $a_1=-1,a_2=1, a_3=-25; a_4=6; a_5=-24$ Thus, we have the sum $=-1+1-2+6-24=-20$

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