What must be true for the radicand of a radical function to find its domain?

To determine the domain of a radical function, particularly when dealing with square roots, the radicand—the expression inside the radical—must meet certain conditions. For square roots, the critical requirement is that the expression must not be negative because the square root of a negative number is not defined within the set of real numbers. This means that the radicand should be zero or positive to ensure that the output of the radical function is a real number.

Therefore, the correct assertion is that the radicand must never become negative. This condition ensures that all possible inputs for the function yield valid outputs, allowing for a complete and defined domain. The radicand being zero would also work since the square root of zero is defined and results in zero, thus still falling within the permissible values.

While having a positive radicand would also suffice for a defined domain, it is more comprehensive to state that the radicand must never be negative, as this includes both zero and positive values, ensuring the entire set of real numbers that the function can accept is accounted for.