20-2x≦0 inequation

Given the inequality:
$$20 - 2 x \leq 0$$
To solve this inequality, we must first solve the corresponding equation:
$$20 - 2 x = 0$$
Solve:
Given the linear equation:

20-2*x = 0

Move free summands (without x)
from left part to right part, we given:
$$- 2 x = -20$$
Divide both parts of the equation by -2

x = -20 / (-2)

$$x_{1} = 10$$
$$x_{1} = 10$$
This roots
$$x_{1} = 10$$
is the points with change the sign of the inequality expression.
First define with the sign to the leftmost point:
$$x_{0} \leq x_{1}$$
For example, let's take the point
$$x_{0} = x_{1} - \frac{1}{10}$$
=
$$- \frac{1}{10} + 10$$
=
$$\frac{99}{10}$$
substitute to the expression
$$20 - 2 x \leq 0$$
$$20 - \frac{2 \cdot 99}{10} \leq 0$$

1/5 <= 0

but

1/5 >= 0

Then
$$x \leq 10$$
no execute
the solution of our inequality is:
$$x \geq 10$$

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