Chapter 8 - Section 8.4 - Equations Quadratic in Form - Exercise Set - Page 635: 4

{$ \pm 2,\pm \sqrt 5$}

Since, $u^2-9u+20=0$ Factorize the expression as follows: $(u-4)(u-5)=0$ or, $u=${$4,5$} Replace $u$ with $x^2$, we have $x^2=4$ and $x^2=5$ This implies that $x= \pm 2,\pm \sqrt 5$ Hence, our solution set is $x=${$ \pm 2,\pm \sqrt 5$}