The equation \( (\cos p - 1)x^2 + (\cos p)x + \sin p = 0 \), where \( x \) is a variable with real roots. Then the interval of \( p \) may be any one of the following:
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For a quadratic equation to have real roots, the discriminant (i.e., \( b^2 - 4ac \)) must be non-negative.