Chapter 5 - Section 5.8 - Solving Equations by Factoring and Problem Solving - Exercise Set - Page 326: 111

-1 and 2 are solutions of the quadratic equation $x^2-x-2=0$.

RECALL: If $(x-a)(x-b)=0$, then $x=a$ and $x=b$ are solutions of the equation $(x-a)(x-b)=0$. Since $-1$ and $2$ are solutions of the quadratic equation, then the equation must be: $(x+1)(x-2)=0$ Multiply the binomials to have: $\\x(x-2) +1(x-2)=0 \\x^2-2x+x-2=0 \\x^2-x-2=0$