SOLUTION: Evaluate: 2cos^2(7pi/12) - 1

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Question 1029655: Evaluate: 2cos^2(7pi/12) - 1
Answer by fractalier(6550) About Me  (Show Source):
You can put this solution on YOUR website!
For this one we can use the identity:
cos%282%2A%28theta%29%29+=+2%2A%28cos%28theta%29%29%5E2+-+1
but we'll go backwards...thus
2cos^2(7pi/12) - 1 = cos(2*(7pi/12)) = cos(7pi/6) = -cos(pi/6) =
-sqrt%283%29+%2F+2