[tex]x= \frac{-b\pm \sqrt{b^2-4ac} }{2a} [/tex] for the equation [tex]ax^2+bx+c[/tex]
Your question is [tex]x^2-2x-8=0[/tex]
So [tex]a=1 \\b=-2\\c=-8[/tex]
So plug in your numbers:
[tex]x= \frac{-(-2)\pm \sqrt{(-2)^2-4(1)(-8)} }{2(1)}[/tex]
Simplify:
[tex]x= \frac{2\pm \sqrt{4-(-32)} }{2}[/tex]
Simplify a little more:
[tex] \frac{2\pm6}{2} [/tex]
So our answer is
[tex]x= \frac{2+ 6 }{2} = 4\\x= \frac{2- 6 }{2}=-2[/tex]
So [tex]x=4, x=-2[/tex]
