Chapter 11 - Section 11.3 - Solving Equations by Using Quadratic Methods - Exercise Set - Page 788: 49

$-2i, 2i, -\sqrt 5, \sqrt 5$

$p^4-p^2-20=0$ $p^2=x$ $p^4-p^2-20=0$ $(p^2)^2-p^2-20=0$ $x^2-x-20=0$ $(x-5)(x+4)=0$ $x-5=0$ $x=5$ $x+4=0$ $x=-4$ $p^2=x$ $p^2=5$ $\sqrt{p^2}=\sqrt 5$ $p=±\sqrt 5$ $p^2=x$ $p^2=-4$ $\sqrt{p^2}=\sqrt{-4}$ $p=±\sqrt {4*-1}$ $p=±2i$