SOLUTION: solve the equation for x in [0,2pi) 4cos^2(x)-4cos(x)=1

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Question 978579: solve the equation for x in [0,2pi)
4cos^2(x)-4cos(x)=1
Answer by josgarithmetic(39630) About Me  (Show Source):
You can put this solution on YOUR website!
4cos%5E2%28x%29-4cos%28x%29-1=0

discriminant is 16+4*4*1=32

cos%28x%29=%284%2B-+sqrt%2832%29%29%2F8

cos%28x%29=%284%2B-+4sqrt%282%29%29%2F8

cos%28x%29=1%2F2%2B-+%281%2F2%29sqrt%282%29

cos(x) is 0.14645 or 0.85355
In quadrant 1 or quadrant 4.
(Arc whose cosine is....)

x is 81.6 degree or 31.4 degree, if in quadrant 1.