## Intermediate Algebra (6th Edition)

$x=\pm 3i$
Isolating the squared variable and then taking the square root of both sides, the solutions of the given quadratic equation, $2x^2+18=0 ,$ are \begin{array}{l}\require{cancel} 2x^2=-18 \\\\ x^2=-\dfrac{18}{2} \\\\ x^2=-9 \\\\ x=\pm\sqrt{-9} \\\\ x=\pm\sqrt{-1}\cdot\sqrt{9} \\\\ x=\pm i\cdot\sqrt{(3)^2} \\\\ x=\pm 3i .\end{array}