 John F.

# Express cos^(4)2x in terms of cosine with an exponent of 1?

Hi, this is my first time using this site.
So I have been staring at this trigonometric equation for a long while and looking for what it asks for. For what I know, I think I have to use sum of difference identities, but I am not so sure where to begin from there. I know I am working for an answer of cosine, but then I am lost as to what identity I should use, or if I am using the right identity.
I really appreciate any help for this problem and I thank you. Kenneth S.

You have not given us an EQUATION.  You have an expression here.

You should know that cos 2x = 2cos2x - 1.
Therefore ½(1+cos 2x) = cos2x

Using this idea, repeatedly, can give you an expression for the 4th power of cosine, in terms of cosine, degree one (the latter's argument being a multiple of the basic argument, x).

Get it?  Good luck.
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02/09/17

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