x+18>90 inequation

Given the inequality:
$$x + 18 > 90$$
To solve this inequality, we must first solve the corresponding equation:
$$x + 18 = 90$$
Solve:
Given the linear equation:

x+18 = 90

Move free summands (without x)
from left part to right part, we given:
$$x = 72$$
$$x_{1} = 72$$
$$x_{1} = 72$$
This roots
$$x_{1} = 72$$
is the points with change the sign of the inequality expression.
First define with the sign to the leftmost point:
$$x_{0} < x_{1}$$
For example, let's take the point
$$x_{0} = x_{1} - \frac{1}{10}$$
=
$$- \frac{1}{10} + 72$$
=
$$\frac{719}{10}$$
substitute to the expression
$$x + 18 > 90$$
$$18 + \frac{719}{10} > 90$$

899     
--- > 90
 10     

Then
$$x < 72$$
no execute
the solution of our inequality is:
$$x > 72$$

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