Chapter 1 - Section 1.3 - Complex Numbers; Quadratic Equations in the Complex Number System - 1.3 Assess Your Understanding - Page 112: 71

$x=2$ or $x=-2$ or $x=\pm 2i$

We solve by factoring: $x^{4}=16$ $x^{4}-16=0$ $(x^{2}-4)(x^{2}+4)=0$ $(x-2)(x+2)(x^{2}+4)=0$ $x-2=0$ or $x+2=0$ or $x^{2}+4=0$ $x=2$ or $x=-2$ or $x^{2}=-4$ $x=2$ or $x=-2$ or $x=\pm\sqrt{-4}$ $x=2$ or $x=-2$ or $x=\pm 2i$ Recall, $i=\sqrt{-1}$