What is the domain of the function #f(x)=sqrt(6 - 2x)#?
In this case you do not want a negative argument for the square root (you cannot find the solution of a negative square root, at least as a real number).
What you do it is to "impose" that the argument is always positive or zero (you know the square root of a positive number or zero).
So you set the argument bigger or equal to zero and solve for
So the values of
Check by yourself substituting for example