Which radical equations produce imaginary values of y for the given values of x?

Question

I don't understand this can someone please explain?

Choices
y=√x, when x<0
y=√4−x, when x≤4
y=√4−x, when x>4
y=√x+8, when x≥−8
√x+8 , when x<−8
y=√x, when x≥0
y=√3x−6, when x<2
y=√3x−6, when x≥2

Answer 1

remember that whatever is under the radical √ cannot be negative

so,
y=√x, when x<0 is not real
y=√4−x, when x>4 is not real, since if x>4, 4-x < 0
and so on for the others

Answer 2

Thank you :)

Answer 3

The answers are: options a, c, e, and g. I already took a test and got 100% with these answers.