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arccos(x-2)
A inequation with variable

The solution

              pi
acos(x - 2) < --
              4 
$$\operatorname{acos}{\left(x - 2 \right)} < \frac{\pi}{4}$$
acos(x - 2) < pi/4
Detail solution
Given the inequality:
$$\operatorname{acos}{\left(x - 2 \right)} < \frac{\pi}{4}$$
To solve this inequality, we must first solve the corresponding equation:
$$\operatorname{acos}{\left(x - 2 \right)} = \frac{\pi}{4}$$
Solve:
$$x_{1} = \frac{\sqrt{2}}{2} + 2$$
$$x_{1} = \frac{\sqrt{2}}{2} + 2$$
This roots
$$x_{1} = \frac{\sqrt{2}}{2} + 2$$
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
$$x_{0} = x_{1} - \frac{1}{10}$$
=
$$- \frac{1}{10} + \left(\frac{\sqrt{2}}{2} + 2\right)$$
=
$$\frac{\sqrt{2}}{2} + \frac{19}{10}$$
substitute to the expression
$$\operatorname{acos}{\left(x - 2 \right)} < \frac{\pi}{4}$$
$$\operatorname{acos}{\left(-2 + \left(\frac{\sqrt{2}}{2} + \frac{19}{10}\right) \right)} < \frac{\pi}{4}$$
    /         ___\     
    |  1    \/ 2 |   pi
acos|- -- + -----| < --
    \  10     2  /   4 
     

but
    /         ___\     
    |  1    \/ 2 |   pi
acos|- -- + -----| > --
    \  10     2  /   4 
     

Then
$$x < \frac{\sqrt{2}}{2} + 2$$
no execute
the solution of our inequality is:
$$x > \frac{\sqrt{2}}{2} + 2$$
         _____  
        /
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       x1
Solving inequality on a graph
Rapid solution
This inequality has no solutions