I'm given the problem cos4x - cos2x = 0. It looks simple, but I I don't know what to do with 4x!

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- Mar 11th 2008, 10:15 PMTessiocos4x
I'm given the problem cos4x - cos2x = 0. It looks simple, but I I don't know what to do with 4x!

- Mar 11th 2008, 11:35 PMMoo
Hello,

You can transform it by using the duplication formula : cos(4x) = cos(2*2x)

Then, you'll explain cos(4x) in terms of cos(2x) and you'll just have to solve an equality with cos(2x) as the variable.

Remember also that if cos(x)=cos(a), x=a + 2pi or x= -a + 2pi