SOLUTION: Given that cos x= 1/4 with x in Quadrant IV, find the exact value of cos(2x). THANKS!

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Question 1070361: Given that cos x= 1/4 with x in Quadrant IV, find the exact value of cos(2x).
THANKS!
Answer by ikleyn(52880) About Me  (Show Source):
You can put this solution on YOUR website!
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Given that cos x= 1/4 with x in Quadrant IV, find the exact value of cos(2x).
THANKS!
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Use the formula


cos(2x) = 2%2Acos%5E2%28x%29-1 = 2%2A%281%2F4%29%5E2-1 = 2%2A%281%2F16%29-1 = 2%2F16-1 = 1%2F8-1 = -7%2F8.


The info "with x in Quadrant IV" is excessive, unnecessary and is not used in the solution.


The result, the answer and the solution would be the same even if x in Quadrant I.