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Ian Fowler
Jun 13, 2020
  ·  Edited: Jun 13, 2020

Here's a little cosine gem

Given: cos(t) = 2/[5*sqrt(5)].

Find the exact value of cos(t/3).


I would have given you the answer, but it's too easy to work backwards using the triple angle formula for cos(3t). I stumbled across the answer when dealing with a different problem.

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Faizan Ahmed
Jun 13, 2020

use calculator and t=79.69 cos(t/3)=0.894

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