Question

X ao quadrado -2x-8=0

Answer 1

x² - 2x - 8 = 0

Δ = b² - 4.a.c 
Δ = -2² - 4 . 1 . -8 
Δ = 4 - 4. 1 . -8 
Δ = 36

Há 2 raízes reais.

x = (-b +- √Δ)/2a

x' = (--2 + √36)/2.1   
x'' = (--2 - √36)/2.1

x' = 8 / 2   
x'' = -4 / 2

x' = 4   
x'' = -2

Answer 2

vamos lá...

x²-2x-8=0

a=1
b=-2
c=-8

Δ=b²-4ac
Δ=(-2)²-4(1)(-8)
Δ=4+32
Δ=36

x= (-b±√Δ)/2a

$x= \frac{-(-2)\pm \sqrt{36} }{2} =~~ \frac{2\pm6}{2} \\ \\ x'= \frac{2+6}{2} = \frac{8}{2} =4 \\ \\ x"= \frac{2-6}{2}=- \frac{4}{2}=-2 \\ \\ V=\{-2,4\}$