SOLUTION: 17. find the exact value of cos 5pi/12

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Question 175837: 17. find the exact value of cos 5pi/12
Answer by Mathtut(3670) About Me  (Show Source):
You can put this solution on YOUR website!
cos(5π/12) = cos(π/6 + π/4)
cos (a + b) = cos a cos b - sin a sin b
cos (π/6 + π/4) = cos π/6 cos π/4 - sin π/6 sin π/4
= √3 / 2 * √2 / 2 - 1/2 * √2 / 2
= √6 / 4 - √2 / 4
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