Chapter 8 - Section 8.4 - Equations Quadratic in Form - Exercise Set - Page 635: 17

{$-5,-2,-1,2$}

Since, $u^2-8u-20=0$ Factorize the expression as follows: $(u-10)(u+2)=0$ or, $u=${$-2,10$} Replace $u$ with $x^2+3x$, we have $x^2+3x=-2 \implies x^2+3x+2=0$ or, $(x+2)(x+1)=0$ $x=${$-2,-1$} and $x^2+3x=10 \implies x^2+3x-10=0$ or, $(x+5)(x-2)=0$ $x=${$2,-5$} Hence, our solution set is $x=${$-5,-2,-1,2$}