Given the inequality:
$$\tan{\left(x \right)} \leq - \frac{1}{3}$$
To solve this inequality, we must first solve the corresponding equation:
$$\tan{\left(x \right)} = - \frac{1}{3}$$
Solve:
Given the equation
$$\tan{\left(x \right)} = - \frac{1}{3}$$
- this is the simplest trigonometric equation
This equation is transformed to
$$x = \pi n + \operatorname{atan}{\left(- \frac{1}{3} \right)}$$
Or
$$x = \pi n - \operatorname{atan}{\left(\frac{1}{3} \right)}$$
, where n - is a integer
$$x_{1} = \pi n - \operatorname{atan}{\left(\frac{1}{3} \right)}$$
$$x_{1} = \pi n - \operatorname{atan}{\left(\frac{1}{3} \right)}$$
This roots
$$x_{1} = \pi n - \operatorname{atan}{\left(\frac{1}{3} \right)}$$
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
$$x_{0} = x_{1} - \frac{1}{10}$$
=
$$\left(\pi n - \operatorname{atan}{\left(\frac{1}{3} \right)}\right) + - \frac{1}{10}$$
=
$$\pi n - \operatorname{atan}{\left(\frac{1}{3} \right)} - \frac{1}{10}$$
substitute to the expression
$$\tan{\left(x \right)} \leq - \frac{1}{3}$$
$$\tan{\left(\pi n - \operatorname{atan}{\left(\frac{1}{3} \right)} - \frac{1}{10} \right)} \leq - \frac{1}{3}$$
-tan(1/10 - pi*n + atan(1/3)) <= -1/3
the solution of our inequality is:
$$x \leq \pi n - \operatorname{atan}{\left(\frac{1}{3} \right)}$$
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