Solving a trig equation

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July 21st 2009, 08:04 AM
mp3qz

Solving a trig equation

Please solve

3./ cos3x - sin 3x + 2cosx = 0
July 22nd 2009, 02:22 PM
pickslides

Quote:

Originally Posted by mp3qz

Please solve

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

Maybe you could consider

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

and

$\cos(3x) = 4\cos^3(x)- 3 \cos(x)$
July 23rd 2009, 08:13 AM
red_dog

Quote:

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

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