Question

-20= -x-x²
s={-5, 4}

Answer 1

$-20=-x-x^2\\x^2+x-20=0$

Coeficientes: a = 1, b = 1 e c = -20

$\Delta=b^2-4ac\\\Delta=1^2-4.1.(-20)\\\Delta=1+80\\\Delta=81$

$x=\frac{-b+-\sqrt{\Delta}}{2a}\\\\x=\frac{-1+-\sqrt{81}}{2.1}\\\\x=\frac{-1+-9}{2}\\\\x_1=\frac{-1+9}{2}=\frac{8}{2}=4\\\\x_2=\frac{-1-9}{2}=\frac{-10}{2}=-5$

Espero ter ajudado.
Bons estudos! :)