can someone help??

f(x)=9x² -2

This is a parabola that opens upward with a vertex at (0, -2). Thus the range is just

[-2, ∞) and since we can substitute anything in for x, the domain is (∞,∞)

f(x)=√(9x² -2)

Since the result of taking a positive square root is always positive or 0, the range is just [0,  ∞). And since we can't have a negative value under the square root, we can just see what makes 9x² - 2 = 0.

9x² -2 = 0

9x² = 2     divide both sides by 9    

x² = 2/9    take the square root of both sides

x = ±√2/3

So the domain is given by (-∞, -√2/3] U [√2/3, ∞)