## Algebra and Trigonometry 10th Edition

Plugging in the different values: $a_1=(-1)^1=-1$ $a_2=(-1)^2=1$ $a_3=(-1)^3=-1$ $a_4=(-1)^4=1$ $a_5=(-1)^5=-1$ $a_5-a_4=-1-1=-2\ne a_4-a_3=1-(-1)=2$, thus this is not an arithmetic sequence.