If f(x) = sqrt x-3, which inequality can be used to find the domain of f(x)?

sqrt x-3 > /= 0
x - 3 > /= 0
sqrt x - 3 = 0
x - 3 = 0

Assuming all of "x-3" is under the square root, then the answer is  which can be written as x - 3 >= 0 which looks like it points to choice B as the answer

The goal is to figure out which x values will make "x-3" nonnegative (not negative). Taking the square root of a negative number leads to a non-real result. So it's a common thing to make the radicand (stuff under the square root) positive or 0.