Chapter 10 - Quadratic Equations - 10.1 - Quadratic Equations - Problem Set 10.1 - Page 442: 23

{$-4,4$}

Using Property 10.1, which states that for any non-negative real number $a$, $x^{2}=a$ can be written as $x=\pm\sqrt a$, we obtain: $4x^{2}=64$ $x^{2}=\frac{64}{4}$ $x^{2}=16$ $x=\pm \sqrt {16}$ $x=\pm 4$ The solution set is {$-4,4$}.