Answer
$a_1= -3, a_2= 6, a_3= -11, a_4= 18, a_5= -27, $ neither .
Work Step by Step
Given $a_n=(-1)^n(n^2+2)$, we have $a_1=(-1)^1(1^2+2)=-3, a_2=(-1)^2(2^2+2)=6, a_3=(-1)^3(3^2+2)=-11, a_4=(-1)^4(4^2+2)=18, a_5=(-1)^5(5^2+2)=-27, $ and we can identify the sequence as neither arithmetic nor geometric.
