Question

Quais dos números -2, 0, 4, são raízes da equação x²- 2x - 8 = 0?
(A) -2 e 1
(B) -2 e 4
(C) -2 e 0
(D) 1 e 4

Answer 1

$x^2-2x-8=0\\\Delta = (-2)^2-4 \cdot 1 \cdot (-8)\\\Delta = 4 +32\\\Delta = 36\\\\x = \dfrac{-(-2)\pm \sqrt{36}}{2 \cdot 1}=\dfrac{2\pm 6}{2}= 1 \pm 3\\\\x_1 = 1-3 = -2\\x_2 = 1+3=4\\\\\boxed{\boxed{c) \ -2 \ e \ 4}}$