Chapter 8 - Section 8.4 - Equations Quadratic in Form - Exercise Set - Page 635: 19

{$\dfrac{-1}{4},\dfrac{1}{5}$}

Since, $u^2-u-20=0$ Factorize the expression as follows: $(u-5)(u+4)=0$ or, $u=${$-4,5$} Replace $u$ with $x^{-1}$, we have $x^{-1}=-4 \implies \dfrac{1}{x}=-4$ $x=\dfrac{-1}{4}$ and $x^{-1}=5 \implies \dfrac{1}{x}=5$ $x=\dfrac{1}{5}$ Hence, our solution set is $x=${$\dfrac{-1}{4},\dfrac{1}{5}$}