Chapter 11 - Section 11.3 - Solving Equations by Using Quadratic Methods - Exercise Set - Page 788: 50

$x=-3, -1, 1, 3$

$x^4-10x^2+9=0$ $x^2=y$ $x^4-10x^2+9=0$ $(x^2)^2-10x^2+9=0$ $y^2-10y+9=0$ $(y-9)(y-1)=0$ $y-9=0$ $y=9$ $y-1=0$ $y=1$ $x^2=y$ $x^2=1$ $\sqrt{x^2}=\sqrt {1}$ $x=±1$ $x^2=y$ $x^2=9$ $\sqrt{x^2}=\sqrt {9}$ $x=±3$