(x-5)(x-1)<0 inequation

Given the inequality:
$$\left(x - 5\right) \left(x - 1\right) < 0$$
To solve this inequality, we must first solve the corresponding equation:
$$\left(x - 5\right) \left(x - 1\right) = 0$$
Solve:
Expand the expression in the equation
$$\left(x - 5\right) \left(x - 1\right) = 0$$
We get the quadratic equation
$$x^{2} - 6 x + 5 = 0$$
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
$$a = 1$$
$$b = -6$$
$$c = 5$$
, then

D = b^2 - 4 * a * c = 

(-6)^2 - 4 * (1) * (5) = 16

Because D > 0, then the equation has two roots.

x1 = (-b + sqrt(D)) / (2*a)

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

or
$$x_{1} = 5$$
$$x_{2} = 1$$
$$x_{1} = 5$$
$$x_{2} = 1$$
$$x_{1} = 5$$
$$x_{2} = 1$$
This roots
$$x_{2} = 1$$
$$x_{1} = 5$$
is the points with change the sign of the inequality expression.
First define with the sign to the leftmost point:
$$x_{0} < x_{2}$$
For example, let's take the point
$$x_{0} = x_{2} - \frac{1}{10}$$
=
$$- \frac{1}{10} + 1$$
=
$$\frac{9}{10}$$
substitute to the expression
$$\left(x - 5\right) \left(x - 1\right) < 0$$
$$\left(-5 + \frac{9}{10}\right) \left(-1 + \frac{9}{10}\right) < 0$$

 41    
--- < 0
100    

but

 41    
--- > 0
100    

Then
$$x < 1$$
no execute
one of the solutions of our inequality is:
$$x > 1 \wedge x < 5$$

         _____  
        /     \  
-------ο-------ο-------
       x2      x1