Given the inequality:
$$\left(\frac{1}{5}\right)^{x} < 4$$
To solve this inequality, we must first solve the corresponding equation:
$$\left(\frac{1}{5}\right)^{x} = 4$$
Solve:
Given the equation:
$$\left(\frac{1}{5}\right)^{x} = 4$$
or
$$-4 + \left(\frac{1}{5}\right)^{x} = 0$$
or
$$\left(\frac{1}{5}\right)^{x} = 4$$
or
$$\left(\frac{1}{5}\right)^{x} = 4$$
- this is the simplest exponential equation
Do replacement
$$v = \left(\frac{1}{5}\right)^{x}$$
we get
$$v - 4 = 0$$
or
$$v - 4 = 0$$
Move free summands (without v)
from left part to right part, we given:
$$v = 4$$
do backward replacement
$$\left(\frac{1}{5}\right)^{x} = v$$
or
$$x = - \frac{\log{\left(v \right)}}{\log{\left(5 \right)}}$$
$$x_{1} = 4$$
$$x_{1} = 4$$
This roots
$$x_{1} = 4$$
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
$$x_{0} = x_{1} - \frac{1}{10}$$
=
$$- \frac{1}{10} + 4$$
=
$$\frac{39}{10}$$
substitute to the expression
$$\left(\frac{1}{5}\right)^{x} < 4$$
$$\left(\frac{1}{5}\right)^{\frac{39}{10}} < 4$$
10___
\/ 5
----- < 4
625
the solution of our inequality is:
$$x < 4$$
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