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x^2-2x-4 equation

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Numerical solution:

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The solution

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 2              
x  - 2*x - 4 = 0
$$\left(x^{2} - 2 x\right) - 4 = 0$$
Detail solution
This equation is of the form
a*x^2 + b*x + c = 0

A quadratic equation can be solved
using the discriminant.
The roots of the quadratic equation:
$$x_{1} = \frac{\sqrt{D} - b}{2 a}$$
$$x_{2} = \frac{- \sqrt{D} - b}{2 a}$$
where D = b^2 - 4*a*c - it is the discriminant.
Because
$$a = 1$$
$$b = -2$$
$$c = -4$$
, then
D = b^2 - 4 * a * c = 

(-2)^2 - 4 * (1) * (-4) = 20

Because D > 0, then the equation has two roots.
x1 = (-b + sqrt(D)) / (2*a)

x2 = (-b - sqrt(D)) / (2*a)

or
$$x_{1} = 1 + \sqrt{5}$$
$$x_{2} = 1 - \sqrt{5}$$
Vieta's Theorem
it is reduced quadratic equation
$$p x + q + x^{2} = 0$$
where
$$p = \frac{b}{a}$$
$$p = -2$$
$$q = \frac{c}{a}$$
$$q = -4$$
Vieta Formulas
$$x_{1} + x_{2} = - p$$
$$x_{1} x_{2} = q$$
$$x_{1} + x_{2} = 2$$
$$x_{1} x_{2} = -4$$
The graph
Rapid solution [src]
           ___
x1 = 1 - \/ 5 
$$x_{1} = 1 - \sqrt{5}$$
           ___
x2 = 1 + \/ 5 
$$x_{2} = 1 + \sqrt{5}$$
x2 = 1 + sqrt(5)
Sum and product of roots [src]
sum
      ___         ___
1 - \/ 5  + 1 + \/ 5 
$$\left(1 - \sqrt{5}\right) + \left(1 + \sqrt{5}\right)$$
=
2
$$2$$
product
/      ___\ /      ___\
\1 - \/ 5 /*\1 + \/ 5 /
$$\left(1 - \sqrt{5}\right) \left(1 + \sqrt{5}\right)$$
=
-4
$$-4$$
-4
Numerical answer [src]
x1 = 3.23606797749979
x2 = -1.23606797749979
x2 = -1.23606797749979