4.4 The Cosine Function and Inverse Cosine Function

. The Cosine Function and Inverse Cosine Function The cosine function is a function with  as its domain and [ , ] - as its range. We write y = cos and y cos or y = arccos( ) to represent the cosine function and the inverse cosine function, respectively. Since cos ) = π is true for all real numbers x and cos x ) need not be equal to cos x for < < π , x ∈  , the period of y = cos is p .