Pre Calculus Repost Please Help

Can someone help me solve this problem:

cos^2x + 5cosx - 2= 0

I am having some trouble finding x

asked by Anonymous
  1. treat it as a quadratic equation where
    cosx = (-5 ± √(25 - 4(1)(-2))/2
    = .37228 or -5.37..
    The second answer lies beyond the range of the cosine function so
    cosx = .37228 and x must be in the first or fourth quadrant.
    x = 68.14 degrees or 291.86 degrees.

    in radians it would be x = 1.18933 or 5.09385

    posted by Reiny

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