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cos(6x)<-(sqrt3/2) inequation

A inequation with variable

The solution

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              ___ 
           -\/ 3  
cos(6*x) < -------
              2   
$$\cos{\left(6 x \right)} < - \frac{\sqrt{3}}{2}$$
cos(6*x) < -sqrt(3)/2
Detail solution
Given the inequality:
$$\cos{\left(6 x \right)} < - \frac{\sqrt{3}}{2}$$
To solve this inequality, we must first solve the corresponding equation:
$$\cos{\left(6 x \right)} = - \frac{\sqrt{3}}{2}$$
Solve:
Given the equation
$$\cos{\left(6 x \right)} = - \frac{\sqrt{3}}{2}$$
- this is the simplest trigonometric equation
This equation is transformed to
$$6 x = \pi n + \operatorname{acos}{\left(- \frac{\sqrt{3}}{2} \right)}$$
$$6 x = \pi n - \pi + \operatorname{acos}{\left(- \frac{\sqrt{3}}{2} \right)}$$
Or
$$6 x = \pi n + \frac{5 \pi}{6}$$
$$6 x = \pi n - \frac{\pi}{6}$$
, where n - is a integer
Divide both parts of the equation by
$$6$$
$$x_{1} = \frac{\pi n}{6} + \frac{5 \pi}{36}$$
$$x_{2} = \frac{\pi n}{6} - \frac{\pi}{36}$$
$$x_{1} = \frac{\pi n}{6} + \frac{5 \pi}{36}$$
$$x_{2} = \frac{\pi n}{6} - \frac{\pi}{36}$$
This roots
$$x_{1} = \frac{\pi n}{6} + \frac{5 \pi}{36}$$
$$x_{2} = \frac{\pi n}{6} - \frac{\pi}{36}$$
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
$$x_{0} = x_{1} - \frac{1}{10}$$
=
$$\left(\frac{\pi n}{6} + \frac{5 \pi}{36}\right) + - \frac{1}{10}$$
=
$$\frac{\pi n}{6} - \frac{1}{10} + \frac{5 \pi}{36}$$
substitute to the expression
$$\cos{\left(6 x \right)} < - \frac{\sqrt{3}}{2}$$
$$\cos{\left(6 \left(\frac{\pi n}{6} - \frac{1}{10} + \frac{5 \pi}{36}\right) \right)} < - \frac{\sqrt{3}}{2}$$
                           ___ 
    /  3   pi       \   -\/ 3  
-sin|- - + -- + pi*n| < -------
    \  5   3        /      2   
                        

but
                           ___ 
    /  3   pi       \   -\/ 3  
-sin|- - + -- + pi*n| > -------
    \  5   3        /      2   
                        

Then
$$x < \frac{\pi n}{6} + \frac{5 \pi}{36}$$
no execute
one of the solutions of our inequality is:
$$x > \frac{\pi n}{6} + \frac{5 \pi}{36} \wedge x < \frac{\pi n}{6} - \frac{\pi}{36}$$
         _____  
        /     \  
-------ο-------ο-------
       x1      x2
Solving inequality on a graph
Rapid solution [src]
   /          /   _____________\           /   _____________\    \
   |          |  /         ___ |           |  /         ___ |    |
   |      atan\\/  7 + 4*\/ 3  /   pi  atan\\/  7 + 4*\/ 3  /    |
And|x < - ---------------------- + --, ---------------------- < x|
   \                3              3             3               /
$$x < - \frac{\operatorname{atan}{\left(\sqrt{4 \sqrt{3} + 7} \right)}}{3} + \frac{\pi}{3} \wedge \frac{\operatorname{atan}{\left(\sqrt{4 \sqrt{3} + 7} \right)}}{3} < x$$
(atan(sqrt(7 + 4*sqrt(3)))/3 < x)∧(x < -atan(sqrt(7 + 4*sqrt(3)))/3 + pi/3)
Rapid solution 2 [src]
     /   _____________\        /   _____________\      
     |  /         ___ |        |  /         ___ |      
 atan\\/  7 + 4*\/ 3  /    atan\\/  7 + 4*\/ 3  /   pi 
(----------------------, - ---------------------- + --)
           3                         3              3  
$$x\ in\ \left(\frac{\operatorname{atan}{\left(\sqrt{4 \sqrt{3} + 7} \right)}}{3}, - \frac{\operatorname{atan}{\left(\sqrt{4 \sqrt{3} + 7} \right)}}{3} + \frac{\pi}{3}\right)$$
x in Interval.open(atan(sqrt(4*sqrt(3) + 7))/3, -atan(sqrt(4*sqrt(3) + 7))/3 + pi/3)