Calculus: Early Transcendentals 8th Edition

$x = -i$ $x = i$ $x = -1$ $x = 1$
$x^4 -1 = 0$ $(x^2 +1)(x^2 -1) = 0$ $(x^2 - (-1)) (x + 1)(x-1) =0$ $(x + i)(x-i)(x+1)(x-1)=0$