Thread: Solving a trig equation

Please solve

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

Originally Posted by mp3qz

Please solve

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

Maybe you could consider

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

and

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

Originally Posted by pickslides

Maybe you could consider

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

and

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

Using the hint of pickslides the equation becomes

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

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