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sin2x=>-(sqrt2/2) inequation

A inequation with variable

The solution

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               ___ 
            -\/ 2  
sin(2*x) >= -------
               2   
$$\sin{\left(2 x \right)} \geq - \frac{\sqrt{2}}{2}$$
sin(2*x) >= -sqrt(2)/2
Detail solution
Given the inequality:
$$\sin{\left(2 x \right)} \geq - \frac{\sqrt{2}}{2}$$
To solve this inequality, we must first solve the corresponding equation:
$$\sin{\left(2 x \right)} = - \frac{\sqrt{2}}{2}$$
Solve:
Given the equation
$$\sin{\left(2 x \right)} = - \frac{\sqrt{2}}{2}$$
- this is the simplest trigonometric equation
This equation is transformed to
$$2 x = 2 \pi n + \operatorname{asin}{\left(- \frac{\sqrt{2}}{2} \right)}$$
$$2 x = 2 \pi n - \operatorname{asin}{\left(- \frac{\sqrt{2}}{2} \right)} + \pi$$
Or
$$2 x = 2 \pi n - \frac{\pi}{4}$$
$$2 x = 2 \pi n + \frac{5 \pi}{4}$$
, where n - is a integer
Divide both parts of the equation by
$$2$$
$$x_{1} = \pi n - \frac{\pi}{8}$$
$$x_{2} = \pi n + \frac{5 \pi}{8}$$
$$x_{1} = \pi n - \frac{\pi}{8}$$
$$x_{2} = \pi n + \frac{5 \pi}{8}$$
This roots
$$x_{1} = \pi n - \frac{\pi}{8}$$
$$x_{2} = \pi n + \frac{5 \pi}{8}$$
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
$$x_{0} = x_{1} - \frac{1}{10}$$
=
$$\left(\pi n - \frac{\pi}{8}\right) + - \frac{1}{10}$$
=
$$\pi n - \frac{\pi}{8} - \frac{1}{10}$$
substitute to the expression
$$\sin{\left(2 x \right)} \geq - \frac{\sqrt{2}}{2}$$
$$\sin{\left(2 \left(\pi n - \frac{\pi}{8} - \frac{1}{10}\right) \right)} \geq - \frac{\sqrt{2}}{2}$$
                            ___ 
    /1   pi         \    -\/ 2  
-sin|- + -- - 2*pi*n| >= -------
    \5   4          /       2   
                         

but
                           ___ 
    /1   pi         \   -\/ 2  
-sin|- + -- - 2*pi*n| < -------
    \5   4          /      2   
                        

Then
$$x \leq \pi n - \frac{\pi}{8}$$
no execute
one of the solutions of our inequality is:
$$x \geq \pi n - \frac{\pi}{8} \wedge x \leq \pi n + \frac{5 \pi}{8}$$
         _____  
        /     \  
-------•-------•-------
       x1      x2
Solving inequality on a graph
Rapid solution 2 [src]
             /   ___________\              /   ___________\     
             |  /       ___ |              |  /       ___ |     
             |\/  2 + \/ 2  |              |\/  2 - \/ 2  |     
[0, pi - atan|--------------|] U [pi - atan|--------------|, pi]
             |   ___________|              |   ___________|     
             |  /       ___ |              |  /       ___ |     
             \\/  2 - \/ 2  /              \\/  2 + \/ 2  /     
$$x\ in\ \left[0, \pi - \operatorname{atan}{\left(\frac{\sqrt{\sqrt{2} + 2}}{\sqrt{2 - \sqrt{2}}} \right)}\right] \cup \left[\pi - \operatorname{atan}{\left(\frac{\sqrt{2 - \sqrt{2}}}{\sqrt{\sqrt{2} + 2}} \right)}, \pi\right]$$
x in Union(Interval(0, pi - atan(sqrt(sqrt(2) + 2)/sqrt(2 - sqrt(2)))), Interval(pi - atan(sqrt(2 - sqrt(2))/sqrt(sqrt(2) + 2)), pi))
Rapid solution [src]
  /   /                      /   ___________\\     /                  /   ___________\     \\
  |   |                      |  /       ___ ||     |                  |  /       ___ |     ||
  |   |                      |\/  2 + \/ 2  ||     |                  |\/  2 - \/ 2  |     ||
Or|And|0 <= x, x <= pi - atan|--------------||, And|x <= pi, pi - atan|--------------| <= x||
  |   |                      |   ___________||     |                  |   ___________|     ||
  |   |                      |  /       ___ ||     |                  |  /       ___ |     ||
  \   \                      \\/  2 - \/ 2  //     \                  \\/  2 + \/ 2  /     //
$$\left(0 \leq x \wedge x \leq \pi - \operatorname{atan}{\left(\frac{\sqrt{\sqrt{2} + 2}}{\sqrt{2 - \sqrt{2}}} \right)}\right) \vee \left(x \leq \pi \wedge \pi - \operatorname{atan}{\left(\frac{\sqrt{2 - \sqrt{2}}}{\sqrt{\sqrt{2} + 2}} \right)} \leq x\right)$$
((0 <= x)∧(x <= pi - atan(sqrt(2 + sqrt(2))/sqrt(2 - sqrt(2)))))∨((x <= pi)∧(pi - atan(sqrt(2 - sqrt(2))/sqrt(2 + sqrt(2))) <= x))