Question: expand trig formulas

I couldn't find a clean expression for cos(x/3) in terms of cos(x) on the web,

is it possible to force maple to expand such a thing in terms of cos(x) ??

I've tried basic things like simply(cos(x/3)), and expand(cos(x/3)) , but it seems like Maple won't know what to do (there's an infinite number of choices here) if I don't TELL it to write it in terms of cos(x) somehow.

 

Is there a way to do such a thing??

 

many thanks.

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