The domain of this function is x = all real numbers.
The two things that typically limit a domain are dividing by zero and taking the square root of a negative. Since neither of these functions or their composite have a square root or a denominator, then you must be able to use all real numbers.
Use the geometric mean for right triangles as the sides are related to the hypotenuse. 30 - 6 = 24. We need that for our proportion. . We cross-multiply to get . Taking the square root of both sides gives us that , the second choice above.