Chapter 9 - Section 9.1 - Solving Quadratic Equations by the Square Root Property - Exercise Set - Page 631: 2

$x=\pm10$

Since $x^2=a$ implies $x=\pm\sqrt{a}$ (the Square Root Property), then the solutions of the given equation, $ x^2=100 ,$ are \begin{array}{l}\require{cancel} x=\pm\sqrt{100} \\\\ x=\pm\sqrt{(10)^2} \\\\ x=\pm10 .\end{array}