Final answer:
The domain of y = sec(x) excludes all points where cosine of x equals zero, which is at x = nπ + π/2 for any integer n, making it the correct choice for the function's domain.
Step-by-step explanation:
The function y = sec(x) is the reciprocal of the cosine function. Since the cosine of x equals zero at x = nπ + π/2, where n is any integer and secant is not defined at these points, the domain of y = sec(x) excludes these values.
Therefore, the correct domain for the secant function is: all real numbers except nπ + π/2, where n is any integer, because at these points, the function would require division by zero, which is undefined.