Math

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Find all real solution of the equation sin^2x = -2+2cosx

  • Math -

    since sin^2 = 1-cos^2,

    1-cos^2 = -2 + 2cos
    cos^2 + 2cos - 3 = 0
    (cos+3)(cos-1) = 0

    cos=1, so x = 0,2pi,4pi,...

    why not -3?

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