Resposta :
[tex]x^2-x-20=0\\\Delta =1-4.1.-20\Rightarrow \Delta =81\\\\x=\frac{1\pm \sqrt{81}}{2}\Rightarrow x_1=5\ ou\ x_2=-4[/tex]
[tex]x^2-x-20=0\\\Delta =1-4.1.-20\Rightarrow \Delta =81\\\\x=\frac{1\pm \sqrt{81}}{2}\Rightarrow x_1=5\ ou\ x_2=-4[/tex]