Trigonometry

Find all solutions of the equation in the interval [0, 2π).
cos(x + 9π) − cos x + 1 = 0

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asked by Thomas
  1. 9/2 =4 1/2
    so 4 times all the way + one time halfway around which is pi
    so you really have cos (x+pi) - cos x + 1 = 0
    but cos (a+b) = cos a cos b - sin a sinb
    so it is
    cos x * (-1) - sin x * (0) - cos x + 1 = 0
    -2 cos x = -1
    cos x = 0.5
    60 and 300 deg

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    posted by Damon

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