Domain is all the possible x values for the equation.
So for this equation, we know that you cannot take the square root of a negative number.
That means, when x-5 = 0 or a negative integer, the equation is no longer possible.
Rearrange x-5 = 0 to find x:
x = 0 + 5
x = 5
And since we know x - 5 cannot equal a negative number, x cannot be less than 5 either.
Therefore, the domain of the equation is x is greater than or equal to 5 (the third option).
