Question

find all values of x for which the fuction y= (sqrrt(x))/(5x-2) is differentiable.

Answer 1

Basically, it's asking for the domain of the function.
Numbers outside of the domain would be places where you either have:

Sqrt or log of a negative number,
Negative number in the denominator,
or other, similar situations.

Answer 2

EDIT:
You can have negative in the denominator, just not 0.