The value of $(i^2-i)(i^2+i)(i^3+i)$ is 

$(i^2-i)(i^2+i)(i^3+i)$

$=(-1-i)(-1+i)(-i+i)(\because i^3=i^2\times i=-1\times i)$

$=(-1-i)(-1+i)\times 0$

$=0$

$\text{'}0\text{'}$ is called neither positive nor negative