Find Cos^4 20° + Cos^4 40° +Cos^4 80°
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Step-by-step explanation:
cos420∘+cos440∘+cos460∘+cos480∘
Suppose that this is a scenario where calculator isn't allowed. I want to say that this expression has something to do with this equation cos220∘+cos240∘+cos260∘+cos280∘=74 but I can't seem to find a method to solve this without relying on brute forcing every term to cos20∘
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