How would I go about solving the equation

cos x = cos 3x ?

I know the equation for cos 2x but this doesn't help - I get $\displaystyle 2cos^2(3x/2) - 1$ which doesn't really help. Is there any other way which it can be done?

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- Mar 11th 2010, 02:42 PMdb5vrySmall trigonometry question
How would I go about solving the equation

cos x = cos 3x ?

I know the equation for cos 2x but this doesn't help - I get $\displaystyle 2cos^2(3x/2) - 1$ which doesn't really help. Is there any other way which it can be done? - Mar 11th 2010, 02:52 PMArchie Meade
- Mar 11th 2010, 02:59 PMKrizalid
or turn $\displaystyle \cos x-\cos3x$ by using sum - product formulae.