## Algebra and Trigonometry 10th Edition

$a_n=(-1)^{n+1}$
$a_1=1=(-1)^2=(-1)^{1+1}$ $a_2=-1=(-1)^3=(-1)^{1+2}$ $a_3=1=(-1)^4=(-1)^{1+3}$ $a_4=-1=(-1)^5=(-1)^{1+4}$ $a_5=1=(-1)^6=(-1)^{1+5}$ It is easy to conclude that: $a_n=(-1)^{n+1}$