Given the inequality:
$$\cot{\left(3 x \right)} > \frac{1}{3}$$
To solve this inequality, we must first solve the corresponding equation:
$$\cot{\left(3 x \right)} = \frac{1}{3}$$
Solve:
Given the equation
$$\cot{\left(3 x \right)} = \frac{1}{3}$$
transform
$$\cot{\left(3 x \right)} - \frac{1}{3} = 0$$
$$\cot{\left(3 x \right)} - \frac{1}{3} = 0$$
Do replacement
$$w = \cot{\left(3 x \right)}$$
Move free summands (without w)
from left part to right part, we given:
$$w = \frac{1}{3}$$
We get the answer: w = 1/3
do backward replacement
$$\cot{\left(3 x \right)} = w$$
substitute w:
$$x_{1} = \frac{\operatorname{acot}{\left(\frac{1}{3} \right)}}{3}$$
$$x_{1} = \frac{\operatorname{acot}{\left(\frac{1}{3} \right)}}{3}$$
This roots
$$x_{1} = \frac{\operatorname{acot}{\left(\frac{1}{3} \right)}}{3}$$
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
$$x_{0} = x_{1} - \frac{1}{10}$$
=
$$- \frac{1}{10} + \frac{\operatorname{acot}{\left(\frac{1}{3} \right)}}{3}$$
=
$$- \frac{1}{10} + \frac{\operatorname{acot}{\left(\frac{1}{3} \right)}}{3}$$
substitute to the expression
$$\cot{\left(3 x \right)} > \frac{1}{3}$$
$$\cot{\left(3 \left(- \frac{1}{10} + \frac{\operatorname{acot}{\left(\frac{1}{3} \right)}}{3}\right) \right)} > \frac{1}{3}$$
-cot(3/10 - acot(1/3)) > 1/3
the solution of our inequality is:
$$x < \frac{\operatorname{acot}{\left(\frac{1}{3} \right)}}{3}$$
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