Which statement is correct about y = cos–1 x? a) if the domain of y = cos x is restricted to (0,π), y = cos-1 x is a function. b) regardless of whether or not the domain of y = cos x is restricted, y = cos–1 x is a function. c) if the domain of y = cos x is restricted to (-π/2, π/2), y = cos-1 x is a function. d) regardless of whether or not the domain of y = cos x is restricted, y = cos–1 x is not a function.