Question

Encontre as raízes da equação:$x^2-4x-5=0$

Answer 1

Completando o quadrado:

$x^2-4x-5=0\\\\x^2-4x=5\\\\x^2-4x+4=9\\\\(x-2)^2=9\\\\\sqrt{(x-2)^2}=\sqrt{9}\\\left|x-2\right|=3~~~~\Longrightarrow~~\left\{\begin{matrix} ~~x-2=-3\\\\ou\\\\ x-2=3 \end{matrix}\right.\\\\x=-1~~ou~~x=5$