# Math Help - Solving a trig equation

1. ## Solving a trig equation

3./ cos3x - sin 3x + 2cosx = 0

2. Originally Posted by mp3qz

3./ cos3x - sin 3x + 2cosx = 0
Maybe you could consider

$\sin(3x) = 3 \sin(x)-4\sin^3(x)$

and

$\cos(3x) = 4\cos^3(x)- 3 \cos(x)$

3. Originally Posted by pickslides
Maybe you could consider

$\sin(3x) = 3 \sin(x)-4\sin^3(x)$

and

$\cos(3x) = 4\cos^3(x)- 3 \cos(x)$
Using the hint of pickslides the equation becomes

$4\sin^3x+4\cos^3x-3\sin x-\cos x=0$

which is the same equation like in this thread: http://www.mathhelpforum.com/math-he...-equation.html