## Elementary and Intermediate Algebra: Concepts & Applications (6th Edition)

$a=\pm i$
Since $x^2=a$ implies $x=\pm\sqrt{a}$ (the Square Root Principle), then the solutions to the given equation, $a^2+1=0 ,$ are \begin{array}{l}\require{cancel} a^2=-1 \\\\ a=\pm\sqrt{-1} \\\\ a=\pm i .\end{array}