Trigonometric Equations
Solve:
[tex]9\tan ^3x=3\tan x[/tex]In the interval [0,2pi)
We have to find all the values of x that make equality stand. First, divide by 3:
[tex]3\tan ^3x=\tan x[/tex]Subtract tan x
[tex]3\tan ^3x-\tan x=0[/tex]Factor tan x out:
[tex]\tan x(3\tan ^2x-1)=0[/tex]One solution comes immediately:
tan x = 0
There are two angles whose tangent is 0:
[tex]x=0\text{ , x=}\pi[/tex]The other solutions come when equating:
[tex]3\tan ^2x-1=0[/tex]Adding 1, and dividing by 3:
[tex]\tan ^2x=\frac{1}{3}[/tex]Taking the square root:
[tex]\tan x=\sqrt[\square]{\frac{1}{3}}=\pm\frac{\sqrt[]{3}}{3}[/tex]The positive answer gives us two solutions:
[tex]\tan x=\frac{\sqrt[]{3}}{3}[/tex]x=pi/6 and x=7pi/6
The negative answer also gives us two solutions:
[tex]\tan x=-\frac{\sqrt[]{3}}{3}[/tex]x=5pi/6, 11pi/6
Summarizing the solutions are:
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