Math - Trigonometry

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Let f(x) be a polynomial such that f(cos theta) = cos(4 theta) for all \theta. Find f(x). (This is essentially the same as finding cos(4 theta) in terms of cos theta; we structure the problem this way so that you can answer as a polynomial. Be sure to write your polynomial with the terms in order of decreasing degree.)
I tried this problem but I don't know if this is correct or not. I got 8 cos^4x + 8 cos^2x + 1. Is this right?
Thanks.

• Math - Trigonometry -

That is correct, good job

• Math - Trigonometry -

Yay thanks man for the help

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